Polymer Composite Separator for a Lithium Secondary Battery and Manufacturing Method

ABSTRACT

A flame-resistant polymer composite separator for use in a lithium battery, wherein the polymer composite separator comprises (a) a binder or matrix polymer; (b) 0.1% to 50% by weight of a lithium salt dispersed in the polymer; and (c) from 30% to 99% by weight of particles or fibers of an inorganic material or polymer fibers that are dispersed in or bonded by the polymer, wherein the polymer is a polymerization or crosslinking product of a reactive additive comprising (i) a first liquid solvent that is polymerizable, (ii) an initiator or crosslinking agent, and (iii) the lithium salt and wherein the polymer composite separator has a thickness from 50 nm to 100 μm and a lithium ion conductivity from 10−8 S/cm to 5×10−2 S/cm at room temperature.

FIELD

The present invention relates to the field of rechargeable lithiumbattery, including the lithium-ion battery and lithium metal battery,and, in particular, to an anode-less rechargeable lithium metal batteryhaving no lithium metal as an anode active material initially when thebattery is made and a method of manufacturing same.

BACKGROUND

Lithium-ion and lithium (Li) metal cells (including Lithium-sulfur cell,Li-air cell, etc.) are considered promising power sources for electricvehicle (EV), hybrid electric vehicle (HEV), and portable electronicdevices, such as lap-top computers and mobile phones. Lithium metal hasthe highest capacity (3,861 mAh/g) compared to any other metal ormetal-intercalated compound (except Li_(4.4)Si) as an anode activematerial. Hence, in general, rechargeable Li metal batteries have asignificantly higher energy density than lithium-ion batteries.

Historically, rechargeable lithium metal batteries were produced usingnon-lithiated compounds having high specific capacities, such as TiS₂,MoS₂, MnO₂, CoO₂ and V₂O₅, as the cathode active materials, which werecoupled with a lithium metal anode. When the battery was discharged,lithium ions were dissolved from the lithium metal anode and transferredto the cathode through the electrolyte and, thus, the cathode becamelithiated. Unfortunately, upon cycling, the lithium metal resulted inthe formation of dendrites that ultimately caused unsafe conditions inthe battery. As a result, the production of these types of secondarybatteries was stopped in the early 1990's giving ways to lithium-ionbatteries.

Even now, cycling stability and safety concerns remain the primaryfactors preventing the further commercialization of Li metal batteriesfor EV, HEV, and microelectronic device applications. These issues areprimarily due to the high tendency for Li to form dendrite structuresduring repeated charge-discharge cycles or an overcharge, leading tointernal electrical shorting and thermal runaway. Many attempts havebeen made to address the dendrite-related issues, as briefly summarizedbelow:

Fauteux, et al. [D. Fauteux, et al., “Secondary Electrolytic Cell andElectrolytic Process,” U.S. Pat. No. 5,434,021, Jul. 18, 1995] appliedto a metal anode a protective surface layer (e.g., a mixture ofpolynuclear aromatic and polyethylene oxide) that enables transfer ofmetal ions from the metal anode to the electrolyte and back. The surfacelayer is also electronically conductive so that the ions will beuniformly attracted back onto the metal anode during electrodeposition(i.e. during battery recharge). Alamgir, et al. [M. Alamgir, et al.“Solid polymer electrolyte batteries containing metallocenes,” U.S. Pat.No. 5,536,599, Jul. 16, 1996] used ferrocenes to prevent chemicalovercharge and dendrite formation in a solid polymer electrolyte-basedrechargeable battery.

Skotheim [T. A. Skotheim, “Stabilized Anode for Lithium-PolymerBattery,” U.S. Pat. No. 5,648,187 (Jul. 15, 1997); U.S. Pat. No.5,961,672 (Oct. 5, 1999)] provided a Li metal anode that was stabilizedagainst the dendrite formation by the use of a vacuum-evaporated thinfilm of a Li ion-conducting polymer interposed between the Li metalanode and the electrolyte. Skotheim, et al. [T. A. Skotheim, et al.“Lithium Anodes for Electrochemical Cells,” U.S. Pat. No. 6,733,924 (May11, 2004); U.S. Pat. No. 6,797,428 (Sep. 28, 2004); U.S. Pat. No.6,936,381 (Aug. 30, 2005); and U.S. Pat. No. 7,247,408 (Jul. 24, 2007)]further proposed a multilayer anode structure consisting of a Limetal-based first layer, a second layer of a temporary protective metal(e.g., Cu, Mg, and Al), and a third layer that is composed of at leastone layer (typically 2 or more layers) of a single ion-conducting glass,such as lithium silicate and lithium phosphate, or polymer. It is clearthat such an anode structure, consisting of at least 3 or 4 layers, istoo complex and too costly to make and use.

Protective coatings for Li anodes, such as glassy surface layers ofLiI—Li₃PO₄—P₂S₅, may be obtained from plasma assisted deposition [S. J.Visco, et al., “Protective Coatings for Negative Electrodes,” U.S. Pat.No. 6,025,094 (Feb. 15, 2000)]. Complex, multi-layer protective coatingswere also proposed by Visco, et al. [S. J. Visco, et al., “ProtectedActive Metal Electrode and Battery Cell Structures with Non-aqueousInterlayer Architecture,” U.S. Pat. No. 7,282,295 (Oct. 16, 2007); U.S.Pat. No. 7,282,296 (Oct. 16, 2007); and U.S. Pat. No. 7,282,302 (Oct.16, 2007)].

Despite these earlier efforts, no rechargeable Li metal batteries haveyet succeeded in the marketplace. This is likely due to the notion thatthese prior art approaches still have major deficiencies. For instance,in several cases, the anode or electrolyte structures are too complex.In others, the materials are too costly or the processes for makingthese materials are too laborious or difficult. Conventional solidelectrolytes typically have a low lithium-ion conductivity, aredifficult to produce and difficult to implement into a battery.

Furthermore, the conventional solid electrolyte, as the sole electrolytein a cell or as an anode-protecting layer (interposed between thelithium film and another electrolyte) does not have and cannot maintaina good contact with the lithium metal. This reduces the effectiveness ofthe electrolyte to support dissolution of lithium ions (during batterydischarge), transport lithium ions, and allowing the lithium ions tore-deposit back to the lithium anode (during battery recharge). Aceramic separator that is disposed between an anode active materiallayer (e.g., a graphite-based anode layer or a lithium metal layer) anda cathode active layer suffers from the same problems as well. Inaddition, a ceramic separator also has a poor contact with the cathodelayer if the electrolyte in the cathode layer is a solid electrolyte(e.g., inorganic solid electrolyte).

Another major issue associated with the lithium metal anode is thecontinuing reactions between liquid electrolyte and lithium metal,leading to repeated formation of “dead lithium-containing species” thatcannot be re-deposited back to the anode and become isolated from theanode. These reactions continue to irreversibly consume electrolyte andlithium metal, resulting in rapid capacity decay. In order to compensatefor this continuing loss of lithium metal, an excessive amount oflithium metal (3-5 times higher amount than what would be required) istypically implemented at the anode when the battery is made. This addsnot only costs but also a significant weight and volume to a battery,reducing the energy density of the battery cell. This important issuehas been largely ignored and there has been no plausible solution tothis problem in battery industry.

Clearly, an urgent need exists for a simpler, more cost-effective, andeasier to implement approach to preventing Li metal dendrite-inducedinternal short circuit and thermal runaway problems in Li metalbatteries, and to reducing or eliminating the detrimental reactionsbetween lithium metal and the electrolyte.

Hence, an object of the present disclosure was to provide an effectiveway to overcome the lithium metal dendrite and reaction problems in alltypes of Li metal batteries having a lithium metal anode. A specificobject of the present disclosure was to provide a lithium cell (eitherlithium-ion cell or lithium metal cell) that exhibits a high specificcapacity, high specific energy, high degree of safety, and a long andstable cycle life.

SUMMARY

The present disclosure provides a flame-resistant polymer compositeseparator for use in a lithium battery, wherein the polymer compositeseparator comprises (a) a binder or matrix polymer; (b) 0.1% to 50% byweight of a lithium salt dispersed in the binder/matrix polymer; and (c)from 30% to 99% by weight ((preferably >60%, more preferably >70%, andfurther preferably >80% by weight) of particles or fibers of aninorganic material or polymer fibers that are dispersed in or bonded bythe binder/matrix polymer, wherein the binder/matrix polymer is apolymerization or crosslinking product of a reactive additive comprising(i) a first liquid solvent that is polymerizable, (ii) an initiator orcrosslinking agent, and (iii) the lithium salt and wherein the polymercomposite separator has a thickness from 50 nm to 100 μm (preferablyfrom 1 to 20 μm and more preferably thinner than 10 μm) and a lithiumion conductivity from 10⁻⁸/cm to 5×10⁻² S/cm at room temperature.

The first liquid solvent is preferably selected from the groupconsisting of vinylene carbonate, ethylene carbonate, fluoroethylenecarbonate, vinyl sulfite, vinyl ethylene sulfite, vinyl ethylenecarbonate, 1,3-propyl sultone, 1,3,5-trioxane (TXE),1,3-acrylic-sultones, methyl ethylene sulfone, methyl vinyl sulfone,ethyl vinyl sulfone, methyl methacrylate, vinyl acetate, acrylamide,1,3-dioxolane (DOL), fluorinated ethers, fluorinated esters, sulfones,sulfides, dinitriles, acrylonitrile (AN), sulfates, siloxanes, silanes,N-methylacetamide, acrylates, ethylene glycols, tetrahydrofuran,combinations thereof, and combinations thereof with phosphates,phosphonates, phosphinates, phosphines, phosphine oxides, phosphonicacids, phosphorous acid, phosphites, phosphoric acids, phosphazenecompounds, ionic liquids, derivatives thereof, and mixtures thereof.

In certain embodiments, the inorganic material comprises particles of aninorganic solid electrolyte material selected from an oxide type,sulfide type, hydride type, halide type, borate type, phosphate type,lithium phosphorus oxynitride (LiPON), Garnet-type, lithium superionicconductor (LISICON) type, sodium superionic conductor (NASICON) type, ora combination thereof.

In some embodiments, the inorganic material particles comprise amaterial selected from a transition metal oxide, aluminum oxide, silicondioxide, transition metal sulfide, transition metal selenide, alkylatedceramic particles, metal phosphate, metal carbonate, or a combinationthereof. Further, the inorganic material fibers may be selected fromceramic fibers, glass fibers, or a combination thereof.

In some embodiments, the polymer fibers comprise polymeric materialsselected from the group consisting essentially of polyacrylonitriles,polyolefins, polyolefin copolymers, polyamides, polyimides, polyvinylalcohol, polyethylene terephthalate, polybutylene terephthalate,polysulfone, polyvinyl fluoride, polyvinylidene fluoride, polyvinylidenefluoride-hexafluoropropylene, polymethyl pentene, polyphenylene sulfide,polyacetyl, polyurethane, aromatic polyamide, semi-aromatic polyamide,polypropylene terephthalate, polymethyl methacrylate, polystyrene,synthetic cellulosic polymers, polyaramids, rigid-rod polymers, ladderpolymers, and blends, mixtures and copolymers including said polymericmaterials.

The lithium salt may be selected from lithium perchlorate, LiClO₄,lithium hexafluorophosphate, LiPF₆, lithium borofluoride, LiBF₄, lithiumhexafluoroarsenide, LiAsF₆, lithium trifluoro-methanesulfonate,LiCF₃SO₃, bis-trifluoromethyl sulfonylimide lithium, LiN(CF₃SO₂)₂,lithium bis(oxalato)borate, LiBOB, lithium oxalyldifluoroborate,LiBF₂C₂O₄, lithium oxalyldifluoroborate, LiBF₂C₂O₄, lithium nitrate,LiNO₃, Li-Fluoroalkyl-Phosphates, LiPF₃(CF₂CF₃)₃, lithiumbisperfluoro-ethylsulfonylimide, LiBETI, lithiumbis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide,lithium trifluoromethanesulfonimide, LiTFSI, an ionic liquid-basedlithium salt, Li₂CO₃, Li₂O, Li₂C₂O₄, LiOH, LiX, ROCO₂Li, HCOLi, ROLi,(ROCO₂Li)₂, (CH₂OCO₂Li)₂, Li₂S, Li_(x)SO_(y), or a combination thereof,wherein X=F, Cl, I, or Br, R=a hydrocarbon group, x=0-1, y=1-4.

In certain desired embodiments, the polymer forms a mixture, blend,copolymer, or interpenetrating network with a lithium ion-conductingpolymer selected from poly(ethylene oxide), polypropylene oxide,polyoxymethylene, polyvinylene carbonate, polypropylene carbonate,poly(ethylene glycol), poly(acrylonitrile), poly(methyl methacrylate),poly(vinylidene fluoride), poly bis-methoxy ethoxyethoxide-phosphazene,polyvinyl chloride, polydimethylsiloxane, poly(vinylidenefluoride)-hexafluoropropylene, cyanoethyl poly(vinyl alcohol), apentaerythritol tetraacrylate-based polymer, an aliphatic polycarbonate,a single Li-ion conducting solid polymer with a carboxylate anion, asulfonylimide anion, or sulfonate anion, poly(ethylene glycol)diacrylate, poly(ethylene glycol) methyl ether acrylate, polyurethane,polyurethan-urea, polyacrylamide, a polyionic liquid, polymerized1,3-dioxolane, polyepoxide ether, polysiloxane,poly(acrylonitrile-butadiene), polynorbornene, poly(hydroxyl styrene),poly(ether ether ketone), polypeptoid, poly(ethylene-maleic anhydride),polycaprolactone, poly(trimethylene carbonate), a copolymer thereof, asulfonated derivative thereof, or a combination thereof.

In certain embodiments, the polymer composite separator furthercomprises a second liquid solvent that permeates into the separatorwherein the second liquid solvent has a higher flash point or lowervapor pressure as compared to the first liquid solvent. Such a secondliquid solvent is capable of improving the lithium-ion conductivityand/or flame-retardancy of the composite separator and the battery cell.

The second liquid solvent may be selected from the group consisting offluoroethylene carbonate, vinyl sulfite, vinyl ethylene sulfite,1,3-propyl sultone, 1,3,5-trioxane (TXE), 1,3-acrylic-sultones, methylethylene sulfone, methyl vinyl sulfone, ethyl vinyl sulfone, methylmethacrylate, vinyl acetate, acrylamide, 1,3-dioxolane (DOL),fluorinated ethers, fluorinated esters, sulfones, sulfides, dinitriles,acrylonitrile (AN), sulfates, siloxanes, silanes, N-methylacetamide,acrylates, ethylene glycols, tetrahydrofuran, combinations thereof, andcombinations thereof with phosphates, phosphonates, phosphinates,phosphines, phosphine oxides, phosphonic acids, phosphorous acid,phosphites, phosphoric acids, phosphazene compounds, ionic liquids,derivatives thereof, and mixtures thereof.

In certain embodiments, the first liquid solvent or the second liquidsolvent is selected from the group consisting of 2-alkoxy (orphenoxy)-2-oxo-1,3,2-dioxaphospholane (I) and 2-alkoxy (orphenoxy)-2-oxo-1,3,2-dioxaphosphorinane (II), derivatives thereof, andcombinations thereof:

The first liquid solvent or the second liquid solvent may be chosen tocomprise phosphate, phosphonate, phosphonic acid, or phosphite selectedfrom TMP, TEP, TFP, TDP, DPOF, DMMP, DMMEMP,tris(trimethylsilyl)phosphite (TTSPi), alkyl phosphate, triallylphosphate (TAP), a combination thereof, wherein TMP, TEP, TFP, TDP,DPOF, DMMP, and DMMEMP have the following chemical formulae:

wherein an end group thereof or a functional group attached thereofcomprises unsaturation for polymerization.

In some embodiments, the first liquid solvent or the second liquidsolvent comprises phosphonate vinyl monomer selected from the groupconsisting of phosphonate bearing allyl monomers, phosphonate bearingvinyl monomers, phosphonate bearing styrenic monomers, phosphonatebearing (meth)acrylic monomers, vinylphosphonic acids, and combinationsthereof. The phosphonate bearing allyl monomer may be selected from aDialkyl allylphosphonate monomer or Dioxaphosphorinane allyl monomer;the phosphonate bearing vinyl monomers is selected from a Dialkyl vinylphosphonate monomer or Dialkyl vinyl ether phosphonate monomer; thephosphonate bearing styrenic monomer is selected from α-, β-, orp-vinylbenzyl phosphonate monomers; or the phosphonate bearing(meth)acrylic monomer is selected from a monomer having a phosphonategroup linked to the acrylate double bond, a phosphonate groups linked tothe ester, or a phosphonate groups linked to the amide.

In certain embodiments, the crosslinking agent comprises a compoundhaving at least one reactive group selected from a hydroxyl group, anamino group, an imino group, an amide group, an acrylic amide group, anamine group, an acrylic group, an acrylic ester group, or a mercaptogroup in the molecule. The crosslinking agent may be selected frompoly(diethanol) diacrylate, poly(ethyleneglycol)dimethacrylate,poly(diethanol) dimethylacrylate, poly(ethylene glycol) diacrylate, or acombination thereof.

The initiator may be selected from an azo compound,azobisisobutyronitrile, azobisisoheptonitrile, dimethylazobisisobutyrate, benzoyl peroxide tert-butyl peroxide and methyl ethylketone peroxide, benzoyl peroxide (BPO), bis(4-tert-butylcyclohexyl)peroxydicarbonate, t-amyl peroxypivalate,2,2′-azobis-(2,4-dimethylvaleronitrile),2,2′-azobis-(2-methylbutyronitrile),1,1-azobis(cyclohexane-1-carbonitrile, benzoylperoxide (BPO), hydrogenperoxide, dodecamoyl peroxide, isobutyryl peroxide, cumenehydroperoxide, tert-butyl peroxypivalate, diisopropyl peroxydicarbonate,lithium hexafluorophosphate (LiPF₆), lithium borofluoride (LiBF₄),lithium hexafluoroarsenide (LiAsF₆), lithium trifluoro-methanesulfonate(LiCF₃SO₃), bis-trifluoromethyl sulfonylimide lithium (LiN(CF₃SO₂)₂),lithium bis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate(LiBF₂C₂O₄), lithium oxalyldifluoroborate (LiBF₂C₂O₄), or a combinationthereof.

In some embodiments, the inorganic material particles are non-uniformlydistributed in the polymer matrix in such a manner that a concentrationof the inorganic material particles in one region of the polymer matrixis greater than a concentration of the inorganic material particles inanother region. For instance, one side of the separator (e.g., the sideto be facing an anode layer) may be designed to contain a higherconcentration of the inorganic particles (e.g., from 60% to 95%) whilethe opposite side (facing the cathode layer) contains a lowerconcentration of the inorganic particles, or vice versa. In someembodiments, in the polymer composite separator, the a concentration ofthe inorganic material particles in one surface region of the polymermatrix is at least 60% by volume (preferably at least 75%, morepreferably at least 85% by volume, further preferably at least 90%, andmost preferably at least 95%) and is greater than the concentration ofthe inorganic material particles in a core region of the polymercomposite separator. The core region preferably contains a second liquidsolvent dispersed therein.

In some preferred embodiments, the particles or fibers of an inorganicmaterial and/or polymer fibers are in a woven or nonwoven fabric form,prior to being impregnated or infiltrated with the polymer.

The present disclosure also provides a lithium secondary batterycomprising a cathode, an anode, and the aforementioned flame-resistantpolymer composite separator, which is disposed between the cathode andthe anode.

In certain embodiments, the anode in the lithium secondary battery hasan amount of lithium or lithium alloy as an anode active materialsupported by an anode current collector. In certain other embodiments,initially the anode has no lithium or lithium alloy as an anode activematerial supported by the anode current collector when the battery ismade and prior to a charge or discharge operation of the battery. Thislatter configuration is referred to as an anode-less lithium battery.During the first battery charge operation, lithium ions come out of thecathode active material, move to the anode, and deposit onto a surfaceof the anode current collector.

In certain embodiments, the battery is a lithium-ion battery and theanode has an anode current collector and a layer of an anode activematerial supported by the anode current collector, wherein the anodeactive materials is selected from the group consisting of: (a) silicon(Si), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), phosphorus(P), bismuth (Bi), zinc (Zn), aluminum (Al), titanium (Ti), nickel (Ni),cobalt (Co), and cadmium (Cd); (b) alloys or intermetallic compounds ofSi, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Ni, Co, or Cd with other elements;(c) oxides, carbides, nitrides, sulfides, phosphides, selenides, andtellurides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Fe, Ni, Co, V, or Cd,and their mixtures, composites, or lithium-containing composites; (d)salts and hydroxides of Sn; (e) lithium titanate, lithium manganate,lithium aluminate, lithium titanium niobium oxide, lithium-containingtitanium oxide, lithium transition metal oxide, ZnCo₂O₄; (f) carbon orgraphite particles (g) prelithiated versions thereof; and (h)combinations thereof.

The anode current collector may be selected from, for instance, a Cufoil, a Cu-coated polymer film, a sheet of Ni foam, a porous layer ofnano-filaments, such as graphene sheets, carbon nanofibers, carbonnano-tubes, etc.

Preferably, the inorganic material comprises an inorganic solidelectrolyte material (dispersed in the thermally stable polymercomposite separator layer) is in a fine powder form having a particlesize preferably from 10 nm to 30 μm, more preferably from 50 nm to 1 μm.The inorganic solid electrolyte material may be selected from an oxidetype, sulfide type, hydride type, halide type, borate type, phosphatetype, lithium phosphorus oxynitride (LiPON), Garnet-type, lithiumsuperionic conductor (LISICON), sodium superionic conductor (NASICON),or a combination thereof. These solid electrolyte particles can improvethe lithium-ion transport rates of the composite separator.

The polymer composite separator preferably has a lithium-ionconductivity no less than 10⁻⁵ S/cm, more preferably no less than 10⁻⁴S/cm, and most preferably no less than 10³ S/cm.

In some embodiments, the inorganic material particles comprise amaterial selected from a transition metal oxide (e.g., TiO₂), aluminumoxide, silicon dioxide, transition metal sulfide, transition metalselenide, alkylated ceramic particles, metal phosphate, metal carbonate,or a combination thereof. These particles act to stop the penetration ofany potential lithium dendrite that otherwise could cause internalshorting.

In some embodiments, this polymer composite layer may be a thin filmdisposed against a surface of an anode current collector. The anodecontains a current collector without a lithium metal or any other anodeactive material, such as graphite or Si particles, when the battery cellis manufactured. Such a battery cell having an initially lithiummetal-free anode is commonly referred to as an “anode-less” lithiumbattery. The lithium ions that are required for shuttling back and forthbetween the anode and the cathode are initially stored in the cathodeactive materials (e.g., Li in LiMn₂O₄ and LiMPO₄, where M=Ni, Co, F, Mn,etc.). During the first battery charge procedure, lithium ions (Li⁺)come out of the cathode active material, move through the electrolyteand then through the presently disclosed protective high-elasticitypolymer layer and get deposited on a surface of the anode currentcollector. As this charging procedure continues, more lithium ions getdeposited onto the current collector surface, eventually forming alithium metal film or coating.

In certain embodiments, the polymer further contains a reinforcementmaterial dispersed therein wherein the reinforcement material isselected from a polymer fiber, a glass fiber, a ceramic fiber ornano-flake (e.g., nano clay flakes), or a combination thereof. Thereinforcement material preferably has a thickness or diameter less than100 nm.

The working electrolyte in the lithium battery may be selected from anorganic liquid electrolyte, ionic liquid electrolyte, polymer gelelectrolyte, solid polymer electrolyte, inorganic solid-stateelectrolyte, quasi-solid electrolyte having a lithium salt dissolved inan organic or ionic liquid with a lithium salt concentration higher than2.0 M, or a combination thereof. The cathode active material may beselected from an inorganic material, an organic material, a polymericmaterial, or a combination thereof. The inorganic material may beselected from a metal oxide, metal phosphate, metal silicide, metalselenide (e.g., lithium polyselides for use in a Li—Se cell), metalsulfide (e.g. lithium polysulfide for use in a Li—S cell), or acombination thereof. Preferably, these cathode active materials containlithium in their structures; otherwise the cathode must contain alithium source.

The inorganic cathode active material may be selected from a lithiumcobalt oxide, lithium nickel oxide, lithium manganese oxide, lithiumvanadium oxide, lithium-mixed metal oxide, lithium iron phosphate,lithium manganese phosphate, lithium vanadium phosphate, lithium mixedmetal phosphate, lithium metal silicide, or a combination thereof.

The cathode active material layer may contain a metal oxide containingvanadium oxide selected from the group consisting of Li_(x)VO₂,Li_(x)V₂O₅, Li_(x)V₃O_(s), Li_(x)V₃O₇, Li_(x)V₄O₉, Li_(x)V₆O₁₃, theirdoped versions, their derivatives, and combinations thereof, wherein0.1<x<5.

The cathode active material layer may contain a metal oxide or metalphosphate, selected from a layered compound LiMO₂, spinel compoundLiM₂O₄, olivine compound LiMPO₄, silicate compound Li₂MSiO₄, Tavoritecompound LiMPO₄F, borate compound LiMBO₃, or a combination thereof,wherein M is a transition metal or a mixture of multiple transitionmetals.

The cathode active material is preferably in a form of nano particle(spherical, ellipsoidal, and irregular shape), nano wire, nano fiber,nano tube, nano sheet, nano belt, nano ribbon, nano disc, nano platelet,or nano horn having a thickness or diameter less than 100 nm. Theseshapes can be collectively referred to as “particles” unless otherwisespecified or unless a specific type among the above species is desired.Further preferably, the cathode active material has a dimension lessthan 50 nm, even more preferably less than 20 nm, and most preferablyless than 10 nm. In some embodiments, one particle or a cluster ofparticles may be coated with or embraced by a layer of carbon disposedbetween the particle(s) and/or a high-elasticity polymer layer (anencapsulating shell).

The cathode layer may further contain a graphite, graphene, or carbonmaterial mixed with the cathode active material particles. The carbon orgraphite material is selected from polymeric carbon, amorphous carbon,chemical vapor deposition carbon, coal tar pitch, petroleum pitch,meso-phase pitch, carbon black, coke, acetylene black, activated carbon,fine expanded graphite particle with a dimension smaller than 100 nm,artificial graphite particle, natural graphite particle, or acombination thereof. Graphene may be selected from pristine graphene,graphene oxide, reduced graphene oxide, graphene fluoride, hydrogenatedgraphene, nitrogenated graphene, functionalized graphene, etc.

The cathode active material particles may be coated with or embraced bya conductive protective coating, which is selected from a carbonmaterial, graphene, electronically conductive polymer, conductive metaloxide, or conductive metal coating.

In certain embodiments, the polymer composite separator layer has twoprimary surfaces with a first primary surface facing the anode side anda second primary surface opposing or opposite to the first primarysurface and wherein the inorganic material particles (e.g., inorganicsolid electrolyte powder) has a first concentration at the first surfaceand a second concentration at the second surface and the firstconcentration is greater than the second concentration. In other words,there are more inorganic particles at the anode side of the polymercomposite layer than the opposite side intended to be facing thecathode. There is a concentration gradient across the thickness of theelastic composite separator layer. The high concentration of inorganicsolid particles on the anode side (preferably >30% by weight and morepreferably >60% by weight) can help stop the penetration of any lithiumdendrite, if formed, and help to form a stable artificialsolid-electrolyte interphase (SEI). Thus, in some embodiments, thecomposite separator has a gradient concentration of the inorganic solidparticles across the thickness of the separator.

The disclosure also provides a process for manufacturing the polymercomposite separator described above, the process comprising (A)dispersing particles or fibers of the inorganic solid material orpolymer fibers and the lithium salt in the first liquid solvent to forma liquid reactive mass or reactive slurry; (B) dispensing and depositinga layer of the liquid reactive mass onto a solid substrate surface; and(C) polymerizing and/or curing the reactive mass to form this layer ofpolymer composite separator.

This reactive mass (a precursor to the desired polymer) may comprise amonomer, an oligomer, or an uncured (but curable) polymer possiblydissolved in a liquid solvent where necessary. This precursor issubsequently cured (polymerized and/or crosslinked).

This solid substrate can be a glass surface, a polymer film surface, ametal foil surface, etc. in order to form a free-standing film for apolymer composite separator. In certain preferred embodiments, the solidsubstrate may be an anode current collector, an anode active materiallayer, or a cathode active material layer. In other words, this polymercomposite separator can be directly deposited onto a layer of anodeactive material, an anode current collector, or a layer of cathodeactive material. This is achievable because curing of the polymer doesnot require a high temperature; curing temperature being typically lowerthan 300° C. or even lower than 100° C. This is in stark contrast to thetypically 900-1,200° C. required of sintering an inorganic solidelectrolyte to form a ceramic separator. In addition, the presentlydisclosed polymer composite separator is at least as good as a ceramicseparator in terms of reducing interfacial impedance and stoppingdendrite penetration.

Preferably, the process is a roll-to-roll process wherein step (B)comprises (i) continuously feeding a layer of the solid substrate (e.g.flexible metal film, plastic film, etc.) from a feeder roller to adispensing zone where the reactive mass is dispensed and deposited ontothe solid substrate to form a continuous layer of the reactive mass;(ii) moving the layer of the reactive mass into a reacting zone wherethe reactive mass is exposed to heat, ultraviolet (UV) light, orhigh-energy radiation (e.g., electron beam) to polymerize and/or curethe reactive mass to form a continuous layer of polymer composite; and(iii) collecting the polymer composite on a winding roller. This processis conducted in a reel-to-reel manner.

The process may further comprise cutting and trimming the layer ofpolymer composite into one or multiple pieces of composite separators.The process may further comprise combining an anode, the polymercomposite separator, an electrolyte, and a cathode electrode to form alithium battery.

The disclosure further provides a process for manufacturing the polymercomposite separator described above, the process comprising (A) forminga woven or nonwoven fabric comprising at least one of the polymer fibersand inorganic material fibers, and optional particles of the inorganicsolid material; (B) dissolving or dispersing the lithium salt and theinitiator or crosslinking agent in the first liquid solvent to form aliquid reactive mass; (C) impregnating or infiltrating a desired amountof the liquid reactive mass into the fabric; and (D) polymerizing and/orcrosslinking said reactive mass to form the layer of polymer compositeseparator. The process may further comprise a step (E) of combining ananode, the woven or nonwoven fabric, and a cathode to form a lithiumbattery cell, wherein step (C) or both steps (C) and (D) are conductedeither before or after step (E).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 Schematic of a prior art lithium metal battery cell, containingan anode layer (a thin Li foil or Li coating deposited on a surface of acurrent collector, Cu foil), a porous separator, and a cathode activematerial layer, which is composed of particles of a cathode activematerial, a conductive additive (not shown) and a resin binder (notshown). A cathode current collector supporting the cathode active layeris also shown.

FIG. 2 Schematic of a presently invented lithium metal battery cell(upper diagram) containing an anode current collector (e.g., Cu foil)but no anode active material (when the cell is manufactured or in afully discharged state), a polymer composite separator, and a cathodeactive material layer, which is composed of particles of a cathodeactive material, a conductive additive (not shown) and a resin binder(not shown). A cathode current collector supporting the cathode activelayer is also shown. The lower diagram shows a thin lithium metal layerdeposited between the Cu foil and the composite separator layer when thebattery is in a charged state.

FIG. 3(A) Schematic of a polymer elastic composite separator layerwherein the inorganic solid electrolyte particles are uniformlydispersed in a matrix of a thermally stable polymer according to someembodiments of the present disclosure.

FIG. 3(B) Schematic of a polymer composite separator layer wherein theinorganic solid electrolyte particles are preferentially dispersed nearone surface (e.g., facing the anode side) of a polymer compositeseparator layer; the opposing surface has a lower or zero concentrationof the inorganic solid electrolyte particles, according to someembodiments of the present disclosure.

FIG. 3(C) Schematic of a polymer composite separator layer wherein theinorganic solid electrolyte particles are preferentially dispersed atthe core of a polymer composite separator layer; the outer regions havea lower or zero concentration of the inorganic solid electrolyteparticles, according to some embodiments of the present disclosure.Alternatively, the core region may have a lower or zero concentration ofthe inorganic solid electrolyte particles, but one or bother outersurface regions have a high concentration (e.g., 60-98% by volume).

FIG. 4 Schematic of a roll-to-roll process for producing rolls ofelastic composite separator in a continuous manner.

FIG. 5(A) flowchart illustrating a process for producing polymercomposite separator according to some embodiments of the disclosure.

FIG. 5(B) flowchart illustrating a process for producing polymercomposite separator according to some alternative embodiments of thedisclosure.

DESCRIPTION

This disclosure is related to a lithium secondary battery, which ispreferably based on a working electrolyte selected from an organicelectrolyte, a polymer gel electrolyte, a solid polymer electrolyte, anionic liquid electrolyte, a quasi-solid electrolyte, or an inorganicsolid-state electrolyte in the anode and/or the cathode. The anode andthe cathode are separated by a solid-state polymer composite separator.The shape of a lithium secondary battery can be cylindrical, square,button-like, etc. The present invention is not limited to any batteryshape or configuration or any type of electrolyte.

The present disclosure provides a flame-resistant polymer compositeseparator for use in a lithium battery, wherein the polymer compositeseparator comprises (a) a binder or matrix polymer (also referred to asthe binder/matrix polymer); (b) 0.1% to 50% by weight of a lithium saltdispersed in the binder/matrix polymer; and (c) from 30% to 99% byweight (preferably >60%, more preferably >70%, and furtherpreferably >80% by weight) of particles or fibers of an inorganicmaterial or polymer fibers that are dispersed in or bonded by thebinder/matrix polymer, wherein the binder/matrix polymer is apolymerization or crosslinking product of a reactive additive comprising(i) a first liquid solvent that is polymerizable, (ii) an initiator orcrosslinking agent, and (iii) the lithium salt and wherein the polymercomposite separator has a thickness from 50 nm to 100 μm (preferablyfrom 1 to 20 μm and more preferably thinner than 10 μm) and a lithiumion conductivity from 10⁻⁸/cm to 5×10⁻² S/cm at room temperature.

This separator can be used in a lithium cell wherein, in a typicalconfiguration, the separator is in ionic contact with both the anode andthe cathode of the battery cell and typically in physical contact withan anode active material layer (or an anode current collector) and witha cathode active material layer.

The first liquid solvent is preferably selected from the groupconsisting of vinylene carbonate, ethylene carbonate, fluoroethylenecarbonate, vinyl sulfite, vinyl ethylene sulfite, vinyl ethylenecarbonate, 1,3-propyl sultone, 1,3,5-trioxane (TXE),1,3-acrylic-sultones, methyl ethylene sulfone, methyl vinyl sulfone,ethyl vinyl sulfone, methyl methacrylate, vinyl acetate, acrylamide,1,3-dioxolane (DOL), fluorinated ethers, fluorinated esters, sulfones,sulfides, dinitriles, acrylonitrile (AN), sulfates, siloxanes, silanes,N-methylacetamide, acrylates, ethylene glycols, tetrahydrofuran,combinations thereof, and combinations thereof with phosphates,phosphonates, phosphinates, phosphines, phosphine oxides, phosphonicacids, phosphorous acid, phosphites, phosphoric acids, phosphazenecompounds, ionic liquids, derivatives thereof, and mixtures thereof.These polymerizable liquid solvents (monomers or curable oligomers) canbe impregnated into a backbone structure (e.g., a layer of nonwovenfabric) of the separator and optionally into the anode and the cathodelayers of a battery cell and then cured (polymerized and/orcrosslinked).

In some embodiments, the binder/matrix polymer forms a mixture, blend,copolymer, or interpenetrating network with a lithium ion-conductingpolymer selected from poly(ethylene oxide), polypropylene oxide,polyoxymethylene, polyvinylene carbonate, polypropylene carbonate,poly(ethylene glycol), poly(acrylonitrile), poly(methyl methacrylate),poly(vinylidene fluoride), poly bis-methoxy ethoxyethoxide-phosphazene,polyvinyl chloride, polydimethylsiloxane, poly(vinylidenefluoride)-hexafluoropropylene, cyanoethyl poly(vinyl alcohol), apentaerythritol tetraacrylate-based polymer, an aliphatic polycarbonate,a single Li-ion conducting solid polymer with a carboxylate anion, asulfonylimide anion, or sulfonate anion, poly(ethylene glycol)diacrylate, poly(ethylene glycol) methyl ether acrylate, polyurethane,polyurethan-urea, polyacrylamide, a polyionic liquid, polymerized1,3-dioxolane, polyepoxide ether, polysiloxane,poly(acrylonitrile-butadiene), polynorbornene, poly(hydroxyl styrene),poly(ether ether ketone), polypeptoid, poly(ethylene-maleic anhydride),polycaprolactone, poly(trimethylene carbonate), a copolymer thereof, asulfonated derivative thereof, or a combination thereof. Mixing,co-polymerizing or semi-IPN formation methods are well-known in the art.For instance, one can simply dissolve the two polymers and/or theirmonomers in a common solvent, following by solvent removal to form apolymer blend. Chemical reaction between chains can be activated whilethese polymers/monomers are in a solution state or a solid mixed state.

The inorganic material may comprise particles of an inorganic solidelectrolyte material selected from an oxide type, sulfide type, hydridetype, halide type, borate type, phosphate type, lithium phosphorusoxynitride (LiPON), Garnet-type, lithium superionic conductor (LISICON)type, sodium superionic conductor (NASICON) type, or a combinationthereof.

In some embodiments, the inorganic material particles comprise amaterial selected from a transition metal oxide, aluminum oxide, silicondioxide, transition metal sulfide, transition metal selenide, alkylatedceramic particles, metal phosphate, metal carbonate, or a combinationthereof. Further, the inorganic material fibers may be selected fromceramic fibers, glass fibers, or a combination thereof. The glassfibers, ceramic fibers, and/or polymer fibers may be made into a wovenor nonwoven fabric as a backbone for the separator. This porous backboneis then impregnated with the binder/matrix polymer.

In some embodiments, the polymer fibers comprise polymeric materialsselected from the group consisting essentially of polyacrylonitriles,polyolefins, polyolefin copolymers, polyamides, polyimides, polyvinylalcohol, polyethylene terephthalate, polybutylene terephthalate,polysulfone, polyvinyl fluoride, polyvinylidene fluoride, polyvinylidenefluoride-hexafluoropropylene, polymethyl pentene, polyphenylene sulfide,polyacetyl, polyurethane, aromatic polyamide, semi-aromatic polyamide,polypropylene terephthalate, polymethyl methacrylate, polystyrene,synthetic cellulosic polymers, polyaramids, rigid-rod polymers, ladderpolymers, and blends, mixtures and copolymers including said polymericmaterials. Aramid fibers are particularly useful polymer fibers due totheir high thermal stability and mechanical strength.

The lithium salt dispersed in the first (polymerizable) liquid solventand thus the subsequently polymerized polymer may be selected fromlithium perchlorate, LiClO₄, lithium hexafluorophosphate, LiPF₆, lithiumborofluoride, LiBF₄, lithium hexafluoroarsenide, LiAsF₆, lithiumtrifluoro-methanesulfonate, LiCF₃SO₃, bis-trifluoromethyl sulfonylimidelithium, LiN(CF₃SO₂)₂, lithium bis(oxalato)borate, LiBOB, lithiumoxalyldifluoroborate, LiBF₂C₂O₄, lithium oxalyldifluoroborate,LiBF₂C₂O₄, lithium nitrate, LiNO₃, Li-Fluoroalkyl-Phosphates,LiPF₃(CF₂CF₃)₃, lithium bisperfluoro-ethylsulfonylimide, LiBETI, lithiumbis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide,lithium trifluoromethanesulfonimide, LiTFSI, an ionic liquid-basedlithium salt, Li₂CO₃, Li₂O, Li₂C₂O₄, LiOH, LiX, ROCO₂Li, HCOLi, ROLi,(ROCO₂Li)₂, (CH₂OCO₂Li)₂, Li₂S, Li_(x)SO_(y), or a combination thereof,wherein X=F, Cl, I, or Br, R=a hydrocarbon group, x=0-1, y=1-4.

In certain embodiments, the polymer composite separator furthercomprises a second liquid solvent that permeates into the separatorwherein the second liquid solvent has a higher flash point or lowervapor pressure as compared to the first liquid solvent. Such a secondliquid solvent is capable of improving the lithium-ion conductivityand/or flame-retardancy of the composite separator and the battery cell.

The second liquid solvent may be selected from the group consisting offluoroethylene carbonate, vinyl sulfite, vinyl ethylene sulfite,1,3-propyl sultone, 1,3,5-trioxane (TXE), 1,3-acrylic-sultones, methylethylene sulfone, methyl vinyl sulfone, ethyl vinyl sulfone, methylmethacrylate, vinyl acetate, acrylamide, 1,3-dioxolane (DOL),fluorinated ethers, fluorinated esters, sulfones, sulfides, dinitriles,acrylonitrile (AN), sulfates, siloxanes, silanes, N-methylacetamide,acrylates, ethylene glycols, tetrahydrofuran, combinations thereof, andcombinations thereof with phosphates, phosphonates, phosphinates,phosphines, phosphine oxides, phosphonic acids, phosphorous acid,phosphites, phosphoric acids, phosphazene compounds, ionic liquids,derivatives thereof, and mixtures thereof.

The present disclosure also provides a lithium secondary batterycomprising a cathode, an anode, and the presently disclosedflame-resistant polymer composite separator, which is disposed betweenthe cathode and the anode.

In certain embodiments, the anode in the lithium secondary battery hasan amount of lithium or lithium alloy as an anode active materialsupported by an anode current collector. In certain other embodiments,initially the anode has no lithium or lithium alloy as an anode activematerial supported by an anode current collector when the battery ismade and prior to a charge or discharge operation of the battery. Thislatter configuration is referred to as an anode-less lithium battery.The current collector may be a Cu foil, a layer of Ni foam, a porouslayer of nano-filaments, such as graphene sheets, carbon nanofibers,carbon nano-tubes, etc. forming a 3D interconnected network ofelectron-conducting pathways.

We have discovered that this polymer composite separator layer providesseveral unexpected benefits: (a) the formation and penetration ofdendrite can be essentially eliminated; (b) uniform deposition oflithium back to the anode side is readily achieved during batterycharging; (c) the layer ensures smooth and uninterrupted transport oflithium ions from/to the anode current collector surface (or the lithiumfilm deposited thereon during the battery operations) and through theinterface between the current collector (or the lithium film depositedthereon) and the polymer composite separator layer with minimalinterfacial resistance; and (d) cycle stability can be significantlyimproved and cycle life increased. No additional protective layer forthe lithium metal anode is required. The separator itself also plays therole as an anode protective layer.

In a conventional lithium metal cell, as illustrated in FIG. 1 , theanode active material (lithium) is deposited in a thin film form or athin foil form directly onto an anode current collector (e.g., a Cufoil) before this anode and a cathode are combined to form a cell. Thebattery is a lithium metal battery, lithium sulfur battery,lithium-selenium battery, etc. As previously discussed in the Backgroundsection, these lithium secondary batteries have the dendrite-inducedinternal shorting and “dead lithium” issues at the anode.

We have solved these challenging issues that have troubled batterydesigners and electrochemists alike for more than 30 years by developingand implementing a new polymer composite separator disposed between theanode (an anode current collector or an anode active material layer) anda cathode active material layer. This polymer composite separator layerhas a lithium ion conductivity no less than 10⁻⁸/cm at room temperature(preferably and more typically from 1×10⁻⁵ S/cm to 5×10⁻² S/cm).

As schematically shown in FIG. 2 , one embodiment of the presentdisclosure is a lithium metal battery cell containing an anode currentcollector (e.g., Cu foil), an anode-protecting layer, a polymercomposite-based separator, and a cathode active material layer. Thecathode active material layer is composed of particles of a cathodeactive material, a conductive additive (not shown) and a resin binder(not shown). A cathode current collector (e.g., Al foil) supporting thecathode active layer is also shown in FIG. 2 .

It may be noted that FIG. 2 shows a lithium battery that initially doesnot contain a lithium foil or lithium coating at the anode (only ananode current collector, such as a Cu foil or a graphene/CNT mat) whenthe battery is made. The needed lithium to be bounced back and forthbetween the anode and the cathode is initially stored in the cathodeactive material (e.g., lithium vanadium oxide Li_(x)V₂O₅, instead ofvanadium oxide, V₂O₅; or lithium polysulfide, instead of sulfur). Duringthe first charging procedure of the lithium battery (e.g., as part ofthe electrochemical formation process), lithium comes out of the cathodeactive material, passes through the elastic composite separator anddeposits on the anode current collector. The presence of the presentlyinvented polymer composite separator (in good contact with the currentcollector) enables the uniform deposition of lithium ions on the anodecurrent collector surface. Such a battery configuration avoids the needto have a layer of lithium foil or coating being present during batteryfabrication. Bare lithium metal is highly sensitive to air moisture andoxygen and, thus, is more challenging to handle in a real batterymanufacturing environment. This strategy of pre-storing lithium in thelithiated (lithium-containing) cathode active materials, such asLi_(x)V₂O₅ and Li₂S_(x), makes all the materials safe to handle in areal manufacturing environment. Cathode active materials, such asLi_(x)V₂O₅ and Li₂S_(x), are typically not air-sensitive.

As the charging procedure continues, more lithium ions get to depositonto the anode current collector, forming a lithium metal film orcoating. During the subsequent discharge procedure, this lithium film orcoating layer decreases in thickness due to dissolution of lithium intothe electrolyte to become lithium ions, creating a gap between thecurrent collector and the protective layer if the separator layer werenot elastic or compliant. Such a gap would make the re-deposition oflithium ions back to the anode impossible during a subsequent rechargeprocedure. We have observed that a selected polymer composite separatorlayer is capable of expanding or shrinking congruently or conformablywith the anode layer. This capability helps to maintain a good contactbetween the current collector (or the lithium film subsequently orinitially deposited on the current collector surface) and the protectivelayer, enabling the re-deposition of lithium ions without interruption.

In certain embodiments, inorganic material particles are non-uniformlydistributed in the thermally stable polymer matrix in such a manner thata concentration of the inorganic material particles in one region of thepolymer matrix is greater than a concentration of the inorganic materialparticles in another region. For instance, FIG. 3(A) schematically showsa polymer composite separator layer wherein inorganic solid materialparticles are uniformly dispersed in a matrix of an elastic polymeraccording to some embodiments of the present disclosure.

According to some other embodiments of the present disclosure, FIG. 3(B)schematically shows a polymer composite separator layer whereininorganic solid electrolyte particles are preferentially dispersed nearone surface (e.g., facing the anode side) of a polymer compositeseparator layer; the opposing surface has a lower or zero concentrationof the inorganic solid electrolyte particles. This latter structure hasthe advantages that the high-concentration portion, being strong andrigid, provides a lithium dendrite-stopping capability while otherportion of the layer remains elastic or compliant to maintain goodcontacts with neighboring layers (e.g., cathode active material layercontaining a solid electrolyte on one side and lithium metal on theother) for reduced interfacial impedance. In some preferred embodiments,this opposing side of the separator contains a second liquid solventdispersed in the polymer matrix.

FIG. 3(C) schematically shows a polymer composite separator layerwherein the inorganic solid electrolyte particles are disposed at thecore of a polymer composite separator layer and the outer regions have alower or zero concentration of the inorganic solid electrolyteparticles, according to some embodiments of the present disclosure. Thesofter outer regions are more conducive to a good contact between theseparator and the anode or the cathode layer, thereby reducing theinterfacial impedance.

Alternatively, the core region may have a lower or zero concentration ofthe inorganic solid electrolyte particles, but one or both outer surfaceregions have a high concentration (e.g., 60-98% by volume) of theparticles. Preferably, the outer surface (intended to be facing thelithium anode layer, for instance) of the polymer composite separatorlayer has a concentration of the inorganic material particles at least60% by volume and the core region contains a desired amount of thesecond liquid solvent.

Preferably, the inorganic solid electrolyte material is in a fine powderform having a particle size preferably from 10 nm to 30 μm (morepreferably from 50 nm to 1 μm). The inorganic solid electrolyte materialmay be selected from an oxide type (e.g., perovskite-type), sulfidetype, hydride type, halide type, borate type, phosphate type, lithiumphosphorus oxynitride (LiPON), Garnet-type, lithium superionic conductor(LISICON), sodium superionic conductor (NASICON), or a combinationthereof.

The inorganic solid electrolytes that can be incorporated into a polymermatrix as an ion-conducting additive to make a separator include, butare not limited to, perovskite-type, NASICON-type, garnet-type andsulfide-type materials. A representative and well-known perovskite solidelectrolyte is Li_(3x)La_(2/3-x)TiO₃, which exhibits a lithium-ionconductivity exceeding 10⁻³ S/cm at room temperature. This material hasbeen deemed unsuitable in lithium batteries because of the reduction ofTi⁴⁺ on contact with lithium metal. However, we have found that thismaterial, when dispersed in an elastic polymer, does not suffer fromthis problem.

The sodium superionic conductor (NASICON)-type compounds include awell-known Na_(1+x)Zr₂Si_(x)P_(3-x)O₁₂. These materials generally havean AM₂(PO₄)₃ formula with the A site occupied by Li, Na or K. The M siteis usually occupied by Ge, Zr or Ti. In particular, the LiTi₂(PO₄)₃system has been widely studied as a solid state electrolyte for thelithium-ion battery. The ionic conductivity of LiZr₂(PO₄)₃ is very low,but can be improved by the substitution of Hf or Sn. This can be furtherenhanced with substitution to form Li_(1+x)M_(x)Ti_(2-x)(PO₄)₃ (M=Al,Cr. Ga, Fe, Sc, In, Lu, Y or La), Al substitution has been demonstratedto be the most effective solid state electrolyte. TheLi_(1+x)Al_(x)Ge_(2-x)(PO₄)₃ system is also an effective solid state dueto its relatively wide electrochemical stability window. NASICON-typematerials are considered as suitable solid electrolytes for high-voltagesolid electrolyte batteries.

Garnet-type materials have the general formula A₃B₂Si₃O₁₂, in which theA and B cations have eightfold and sixfold coordination, respectively.In addition to Li₃M₂Ln₃O₁₂ (M=W or Te), a braod series of garnet-typematerials may be used as an additive, including Li₅La₃M₂O₁₂ (M=Nb orTa), Li₆ALa₂M₂O₁₂ (A=Ca, Sr or Ba; M=Nb or Ta),Li_(5.5)La₃M_(1.75)B_(0.25)O₁₂ (M=Nb or Ta; B=In or Zr) and the cubicsystems Li₇La₃Zr₂O₁₂ and Li_(7.06)M₃Y_(0.06)Zr_(1.94)O₁₂ (M=La, Nb orTa). The Li_(6.5)La₃Zr_(1.75)Te_(0.25)O₁₂ compounds have a high ionicconductivity of 1.02×10⁻³ S/cm at room temperature.

The sulfide-type solid electrolytes include the Li₂S—SiS₂ system. Thehighest reported conductivity in this type of material is 6.9×10⁻⁴ S/cm,which was achieved by doping the Li₂S—SiS₂ system with Li₃PO₄. Thesulfide type also includes a class of thio-LISICON (lithium superionicconductor) crystalline material represented by the Li₂S—P₂S₅ system. Thechemical stability of the Li₂S—P₂S_(s) system is considered as poor, andthe material is sensitive to moisture (generating gaseous H₂S). Thestability can be improved by the addition of metal oxides. The stabilityis also significantly improved if the Li₂S—P₂S₅ material is dispersed inan elastic polymer.

These solid electrolyte particles dispersed in a polymer matrix orbonded together by a polymer binder can help stop the penetration oflithium dendrites (if present) and enhance the lithium-ion conductivityof certain polymers having an intrinsically low ion conductivity.

Preferably and typically, the disclosed binder/matrix polymer has alithium-ion conductivity no less than 10⁻⁵ S/cm, more preferably no lessthan 10⁻⁴ S/cm, further preferably no less than 10⁻³ S/cm, and mostpreferably no less than 10⁻² S/cm. Preferably, the composite separatoris a polymer matrix composite containing from 1% to 99% (preferably 30%to 95% and most preferably 60% to 90%) by weight of lithiumion-conducting solid electrolyte particles dispersed in or bonded by apolymer matrix material.

Typically, a selected matrix/binder polymer is originally in a monomeror oligomer state that can be polymerized into a linear or branchedpolymer or cured to form a cross-linked polymer. Alternatively, prior tocuring, the polymers or oligomers are soluble in an organic solvent toform a polymer solution. An ion-conducting additive may be added to thissolution to form a suspension. This solution or suspension can then beformed into a thin layer of polymer precursor on a surface of an anodecurrent collector or a solid substrate surface. The polymer precursor(e.g., monomer and initiator or oligomer and a crosslinker, etc.) isthen polymerized and/or cured to form a cross-linked polymer. This thinlayer of polymer may be tentatively deposited on a solid substrate(e.g., surface of a polymer or glass), dried, and separated from thesubstrate to become a free-standing polymer layer. This free-standinglayer is then laid on a lithium foil/coating or implemented between ananode layer (e.g., a Si-based anode active material layer or a lithiumfilm/coating) and a cathode layer. Polymer layer formation can beaccomplished by using one of several procedures well-known in the art;e.g., spraying, spray-painting, printing, coating, extrusion-basedfilm-forming, casting, etc.

In the conventional lithium-ion battery or lithium metal batteryindustry, the liquid solvents listed above as choices of the firstliquid solvent are commonly used as a solvent to dissolve a lithium salttherein and the resulting solutions are used as a liquid electrolyte.These liquid solvents typically have a relatively high dielectricconstant and are capable of dissolving a high amount of a lithium salt;however, they are typically highly volatile, having a low flash pointand being highly flammable. Further, these liquid solvents are generallynot known to be polymerizable, with or without the presence of a secondliquid solvent, and a separate or different polymer or monomer istypically used in the industry to prepare a gel polymer electrolyte orsolid polymer electrolyte.

It is highly advantageous to be able to polymerize the liquid solventonce the liquid electrolyte (having a lithium salt dissolved in thefirst liquid solvent) is injected into a battery cell or into theseparator layer backbone structure (e.g., a woven or nonwoven fabriccontaining polymeric, glass, and/or ceramic fibers). With such aninnovative strategy, one can readily reduce the liquid solvent amount orcompletely eliminate the volatile liquid solvent all together. A desiredamount of a second liquid solvent, preferably a flame-resistant liquidsolvent, may be retained in the battery cell to improve the lithium-ionconductivity of the electrolyte. Desirable flame retardant-type secondliquid solvents are, as examples, alkyl phosphates, alkyl phosphonates,phosphazenes, hydrofluoroethers, fluorinated ethers, and fluorinatedesters.

This strategy enables us to achieve several desirable features of theresultant electrolytes and batteries:

-   -   a) no liquid electrolyte leakage issue (the in situ cured        polymer being capable of holding the remaining liquid together        to form a gel);    -   b) adequate lithium salt amount can be dissolved in the        electrolyte, enabling a good lithium ion conductivity;    -   c) reduced or eliminated flammability (only a solid polymer and,        optionally, a non-flammable second liquid are retained in the        cell);    -   d) good ability of the electrolyte to wet the anode/cathode        active material surfaces (hence, significantly reduced        interfacial impedance and internal resistance);    -   e) processing ease and compatibility with current lithium-ion        battery production processes and equipment, etc.; and    -   f) enabling a high cathode active material proportion in the        cathode electrode (typically 75-97%, in contrast to typically        less than 75% by weight of the cathode active material when        working with a conventional solid polymer electrolyte or        inorganic solid electrolyte.        This disclosed in situ-cured polymer electrolyte approach is of        significant utility value since most of the organic solvents in        the lithium-ion cell electrolytes are known to be volatile and        flammable, posing a fire and explosion danger. Further, current        solid-state electrolytes are not compatible with existing        lithium-ion battery manufacturing equipment and processes.

In certain preferred embodiments, the second liquid solvent comprises aflame-resisting or flame-retardant liquid selected from an organicphosphorus compound, an inorganic phosphorus compound, a halogenatedderivative thereof, or a combination thereof. The organic phosphoruscompound or the inorganic phosphorus compound preferably is selectedfrom the group consisting of phosphates, phosphonates, phosphonic acids,phosphorous acids, phosphites, phosphoric acids, phosphinates,phosphines, phosphine oxides, phosphazene compounds, derivativesthereof, and combinations thereof.

Thus, in certain embodiments, the second liquid solvent is selected fromthe group consisting of fluorinated ethers, fluorinated esters,sulfones, sulfides, nitriles, sulfates, siloxanes, silanes, phosphates,phosphonates, phosphinates, phosphines, phosphine oxides, phosphonicacids, phosphorous acid, phosphites, phosphoric acids, phosphazenecompounds, derivatives thereof, and combinations thereof.

In some embodiments, the second liquid solvent is selected from aphosphate, phosphonate, phosphinate, phosphine, or phosphine oxidehaving the structure of:

wherein R¹⁰, R¹¹, and R¹², are independently selected from the groupconsisting of alkyl, aryl, heteroalkyl, heteroaryl, halogen substitutedalkyl, halogen substituted aryl, halogen substituted heteroalkyl,halogen substituted heteroaryl, alkoxy, aryloxy, heteroalkoxy,heteroaryloxy, halogen substituted alkoxy, halogen substituted aryloxy,halogen substituted heteroalkoxy, and halogen substituted heteroaryloxyfunctional groups, and the second liquid solvent is stable under anapplied electrical potential no less than 4 V.

In some embodiments, the second liquid solvent comprises aphosphoranamine having the structure of:

wherein R¹, R², and R³ are independently selected from the groupconsisting of alkyl, aryl, heteroalkyl, heteroaryl, halogen substitutedalkyl, halogen substituted aryl, halogen substituted heteroalkyl,halogen substituted heteroaryl, alkoxy, aryloxy, heteroalkoxy,heteroaryloxy, halogen substituted alkoxy, halogen substituted aryloxy,halogen substituted heteroalkoxy, and halogen substituted heteroaryloxyfunctional groups, wherein R¹, R², and R³ are represented by at leasttwo different substituents and wherein X is selected from the groupconsisting of an organosiylyl group or a tert-butyl group. The R¹, R²,and R³ may be each independently selected from the group consisting ofan alkoxy group, and an aryloxy group.

The cathode may contain a cathode active material (along with anoptional conductive additive and an optional resin binder) and anoptional cathode current collector (such as Al foil) supporting thecathode active material. The anode may have an anode current collector,with or without an anode active material in the beginning when the cellis made. It may be noted that if no conventional anode active material,such as graphite, Si, SiO, Sn, and conversion-type anode materials, andno lithium metal is present in the cell when the cell is made and beforethe cell begins to charge and discharge, the battery cell is commonlyreferred to as an “anode-less” lithium cell.

It may be noted that these first liquid solvents herein disclosed, uponpolymerization, become essentially non-flammable. These liquid solventswere typically known to be useful for dissolving a lithium salt and notknown for their polymerizability or their potential as an electrolytepolymer.

In some preferred embodiments, the battery cell contains substantiallyno volatile liquid solvent therein after polymerization. However, it isessential to initially include a liquid solvent in the cell, enablingthe lithium salt to get dissociated into lithium ions and anions. Amajority (>50%, preferably >70%) or substantially all of theunpolymerized first liquid solvent (particularly the organic solvent) isthen removed just before or after curing of the reactive additive. Withsubstantially 0% liquid solvent, the resulting electrolyte is asolid-state electrolyte. With less than 30% liquid solvent, we have aquasi-solid electrolyte. Both are highly flame-resistant.

In certain embodiments, the electrolyte exhibits a vapor pressure lessthan 0.001 kPa when measured at 20° C., a vapor pressure less than 60%of the vapor pressure of the combined first liquid solvent and lithiumsalt alone prior to polymerization, a flash point at least 100 degreesCelsius higher than a flash point of the liquid solvent prior topolymerization, a flash point higher than 200° C., or no measurableflash point and wherein the polymer has a lithium ion conductivity from10⁻⁸ S/cm to 10⁻² S/cm at room temperature.

A lower proportion of the unpolymerized liquid solvent in theelectrolyte leads to a significantly reduced vapor pressure andincreased flash point or completely eliminated flash point(un-detectable). Although typically by reducing the liquid solventproportion one tends to observe a reduced lithium-ion conductivity forthe resulting electrolyte; however, quite surprisingly, after athreshold liquid solvent fraction, this trend is diminished or reversed(the lithium-ion conductivity can actually increase with reduced liquidsolvent in some cases).

In certain embodiments, the reactive additive comprises a firstpolymerizable liquid solvent and a second liquid solvent and wherein thesecond liquid solvent either is not polymerizable or is polymerizablebut polymerized to a lesser extent as compared to the firstpolymerizable liquid solvent. The presence of this second liquid solventis designed to impart certain desired properties to the polymerizedelectrolyte, such as lithium-ion conductivity, flame retardancy, abilityof the electrolyte to permeate into the electrode (anode and/or cathode)to properly wet the surfaces of the anode active material and/or thecathode active material.

In some embodiments, the second liquid solvent is selected from afluorinated carbonate, hydrofluoroether, fluorinated ester, sulfone,nitrile, phosphate, phosphite, alkyl phosphonate, phosphazene, sulfate,siloxane, silane, 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME),tetraethylene glycol dimethylether (TEGDME), poly(ethylene glycol)dimethyl ether (PEGDME), diethylene glycol dibutyl ether (DEGDBE),2-ethoxyethyl ether (EEE), sulfone, sulfolane, ethylene carbonate (EC),dimethyl carbonate (DMC), methylethyl carbonate (MEC), diethyl carbonate(DEC), ethyl propionate, methyl propionate, propylene carbonate (PC),gamma.-butyrolactone (Y-BL), acetonitrile (AN), ethyl acetate (EA),propyl formate (PF), methyl formate (MF), toluene, xylene, methylacetate (MA), fluoroethylene carbonate (FEC), vinylene carbonate (VC),allyl ethyl carbonate (AEC), or a combination thereof.

Desirable polymerizable liquid solvents can include fluorinated monomershaving unsaturation (double bonds or triple bonds) in the backbone orcyclic structure (e.g., fluorinated vinyl carbonates, fluorinated vinylmonomers, fluorinated esters, fluorinated vinyl esters, and fluorinatedvinyl ethers). These chemical species may also be used as a secondliquid solvent in the presently disclosed electrolyte. Fluorinated vinylesters include R_(f)CO₂CH═CH₂ and Propenyl Ketones, R_(f)COCH═CHCH₃,where Rr is F or any F-containing functional group (e.g., CF₂— andCF₂CF₃—).

Two examples of fluorinated vinyl carbonates are given below:

These liquid solvents, as a monomer, can be cured in the presence of aninitiator (e.g., 2-Hydroxy-2-methyl-1-phenyl-propan-1-one, CibaDAROCUR-1173, which can be activated by UV or electron beam):

In some embodiments, the fluorinated carbonate is selected from vinyl-or double bond-containing variants of fluoroethylene carbonate (FEC),DFDMEC, FNPEC, hydrofluoro ether (HFE), trifluoro propylene carbonate(FPC), or methyl nonafluorobutyl ether (MFE), wherein the chemicalformulae for FEC, DFDMEC, and FNPEC, respectively are shown below:

Desirable sulfones as a polymerizable first liquid solvent or as asecond liquid solvent include, but not limited to, alkyl and aryl vinylsulfones or sulfides; e.g., ethyl vinyl sulfide, allyl methyl sulfide,phenyl vinyl sulfide, phenyl vinyl sulfoxide, ethyl vinyl sulfone, allylphenyl sulfone, allyl methyl sulfone, and divinyl sulfone.

Simple alkyl vinyl sulfones, such as ethyl vinyl sulfone, may bepolymerized via emulsion and bulk methods. Propyl vinyl sulfone may bepolymerized by alkaline persulfate initiators to form soft polymers. Itmay be noted that aryl vinyl sulfone, e.g., naphthyl vinyl sulfone,phenyl vinyl sulfone, and parra-substituted phenyl vinyl sulfone (R=NH₂,NO₂ or Br), were reported to be unpolymerizable with free-radicalinitiators. However, we have observed that phenyl and methyl vinylsulfones can be polymerized with several anionic-type initiators.Effective anionic-type catalysts or initiators are n-BuLi, ZnEt₂,LiN(CH₂)₂, NaNH₂, and complexes of n-LiBu with ZnEt₂ or AlEh. A secondsolvent, such as pyridine, sulfolane, toluene or benzene, can be used todissolve alkyl vinyl sulfones, aryl vinyl sulfones, and other largersulfone molecules.

In certain embodiments, the sulfone is selected from TrMS, MTrMS, TMS,or vinyl or double bond-containing variants of TrMS, MTrMS, TMS, EMS,MMES, EMES, EMEES, or a combination thereof; their chemical formulaebeing given below:

The cyclic structure, such as TrMS, MTrMS, and TMS, can be polymerizedvia ring-opening polymerization with the assistance of an ionic typeinitiator.

The nitrile may be selected from AND, GLN, SEN, or a combination thereofand their chemical formulae are given below:

In some embodiments, the phosphate (including various derivatives ofphosphoric acid), alkyl phosphonate, phosphazene, phosphite, or sulfateis selected from tris(trimethylsilyl) phosphite (TTSPi), alkylphosphate, triallyl phosphate (TAP), ethylene sulfate (DTD), acombination thereof, or a combination with 1,3-propane sultone (PS) orpropene sultone (PES). The phosphate, alkyl phosphonate, or phosphazenemay be selected from the following:

wherein R=H, NH₂, or C₁-C₆ alkyl.

Phosphonate moieties can be readily introduced into vinyl monomers toproduce allyl-type, vinyl-type, styrenic-type and (meth)acrylic-typemonomers bearing phosphonate groups (e.g., either mono orbisphosphonate). These liquid solvents may serve as a first or a secondliquid solvent in the electrolyte composition. The phosphate, alkylphosphonate, phosphonic acid, and phosphazene, upon polymerization, arefound to be essentially non-flammable. Good examples include diethylvinylphosphonate demethyl vinylphosphonate, vinylphosphonic acid,diethyl allyl phosphate, and diethyl allylphosphonate:

Examples of initiator compounds that can be used in the polymerizationof vinylphosphonic acid are peroxides such as benzoyl peroxide, toluyperoxide, di-tert.butyl peroxide, chloro benzoyl peroxide, orhydroperoxides such as methylethyl ketone peroxide, tert, butylhydroperoxide, cumene hydroperoxide, hydrogen Superoxide, orazo-bis-iso-butyro nitrile, or sulfinic acids such asp-methoxyphenyl-sulfinic acid, isoamyl-sulfinic acid, benzene-sulfinicacid, or combinations of various of such catalysts with one anotherand/or combinations for example, with formaldehyde sodium sulfoxylate orwith alkali metal sulfites.

The siloxane or silane may be selected from alkylsiloxane (Si—O),alkyylsilane (Si—C), liquid oligomeric silaxane (—Si—O—Si—), or acombination thereof.

The reactive additive may further comprise an amide group selected fromN,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylformamide,N,N-diethylformamide, or a combination thereof.

In certain embodiments, the crosslinking agent comprises a compoundhaving at least one reactive group selected from a hydroxyl group, anamino group, an imino group, an amide group, an acrylic amide group, anamine group, an acrylic group, an acrylic ester group, or a mercaptogroup in the molecule.

In certain embodiments, the crosslinking agent is selected frompoly(diethanol) diacrylate, poly(ethyleneglycol)dimethacrylate,poly(diethanol) dimethylacrylate, poly(ethylene glycol) diacrylate,lithium hexafluorophosphate (LiPF₆), lithium borofluoride (LiBF₄),lithium hexafluoroarsenide (LiAsF₆), lithium trifluoro-methanesulfonate(LiCF₃SO₃), bis-trifluoromethyl sulfonylimide lithium (LiN(CF₃SO₂)₂),lithium bis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate(LiBF₂C₂O₄), lithium oxalyldifluoroborate (LiBF₂C₂O₄), or a combinationthereof.

The initiator may be selected from an azo compound (e.g.,azodiisobutyronitrile, AIBN), azobisisobutyronitrile,azobisisoheptonitrile, dimethyl azobisisobutyrate, benzoyl peroxidetert-butyl peroxide and methyl ethyl ketone peroxide, benzoyl peroxide(BPO), bis(4-tert-butylcyclohexyl)peroxydicarbonate, t-amylperoxypivalate, 2,2′-azobis-(2,4-dimethylvaleronitrile),2,2′-azobis-(2-methylbutyronitrile),1,1-azobis(cyclohexane-1-carbonitrile, benzoylperoxide (BPO), hydrogenperoxide, dodecamoyl peroxide, isobutyryl peroxide, cumenehydroperoxide, tert-butyl peroxypivalate, diisopropyl peroxydicarbonate,or a combination thereof.

The crosslinking agent may comprise a compound having at least onereactive group selected from a hydroxyl group, an amino group, an iminogroup, an amide group, an amine group, an acrylic group, or a mercaptogroup in the molecule. The amine group is preferably selected fromChemical Formula 2:

In the rechargeable lithium battery, the reactive additive (to be curedinto a polymer) may further comprise a chemical species represented byChemical Formula 3 or a derivative thereof and the crosslinking agentcomprises a chemical species represented by Chemical Formula 4 or aderivative thereof:

where R₁ is hydrogen or methyl group, and R₂ and R₃ are eachindependently one selected from the group consisting of hydrogen,methyl, ethyl, propyl, diallylaminopropyl (—C₃H₆N(R′)₂) and hydroxyethyl(CH₂ CH₂ OH) groups, and R₄ and R₅ are each independently hydrogen ormethyl group, and n is an integer from 3 to 30, wherein R′ is C₁-C₅alkyl group.

Examples of suitable vinyl monomers having Chemical formula 3 includeacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide,N-isopropylacrylamide, N,N-dimethylamino-propylacrylamide, andN-acryloylmorpholine. Among these species, N-isopropylacrylamide andN-acryloylmorpholine are preferred.

The crosslinking agent is preferably selected from N,N-methylenebisacrylamide, epichlorohydrin, 1,4-butanediol diglycidyl ether,tetrabutylammonium hydroxide, cinnamic acid, ferric chloride, aluminumsulfate octadecahydrate, diepoxy, dicarboxylic acid compound,poly(potassium 1-hydroxy acrylate) (PKHA), glycerol diglycidyl ether(GDE), ethylene glycol, polyethylene glycol, polyethylene glycoldiglycidyl ether (PEGDE), citric acid (Formula 4 below), acrylic acid,methacrylic acid, a derivative compound of acrylic acid, a derivativecompound of methacrylic acid (e.g, polyhydroxyethylmethacrylate),glycidyl functions, N,N′-Methylenebisacrylamide (MBAAm), Ethylene glycoldimethacrylate (EGDMAAm), isobornyl methacrylate, poly (acrylic acid)(PAA), methyl methacrylate, isobornyl acrylate, ethyl methacrylate,isobutyl methacrylate, n-Butyl methacrylate, ethyl acrylate, 2-Ethylhexyl acrylate, n-Butyl acrylate, a diisocyanate (e.g. methylenediphenyl diisocyanate, MDI), an urethane chain, a chemical derivativethereof, or a combination thereof.

Preferably, the lithium salt occupies 0.1%-30% by weight and thecrosslinking agent and/or initiator occupies 0.1-50% by weight of thereactive polymer precursor.

It may be advantageous for these materials to form a lightlycross-linked network of polymer chains. In other words, the networkpolymer or cross-linked polymer should have a relatively low degree ofcross-linking or low cross-link density to impart a high elasticdeformation. The polymer may contain a simultaneous interpenetratingnetwork (SIN) polymer, wherein two cross-linking chains intertwine witheach other, or a semi-interpenetrating network polymer (semi-IPN), whichcontains a cross-linked polymer and a linear polymer.

The aforementioned polymer can be mixed with a broad array ofelastomers, lithium ion-conducting materials, and/or strengtheningmaterials (e.g., glass fibers, ceramic fibers or particles, polymerfibers, such as aramid fibers).

A broad array of elastomers can be mixed with a thermally stable polymerto form a blend, co-polymer, or interpenetrating network that serves tobond the inorganic solid particles together as a separator layer. Theelastomeric material may be selected from natural polyisoprene (e.g.cis-1,4-polyisoprene natural rubber (NR) and trans-1,4-polyisoprenegutta-percha), synthetic polyisoprene (IR for isoprene rubber),polybutadiene (BR for butadiene rubber), chloroprene rubber (CR),polychloroprene (e.g. Neoprene, Baypren etc.), butyl rubber (copolymerof isobutylene and isoprene, IIR), including halogenated butyl rubbers(chloro butyl rubber (CUR) and bromo butyl rubber (BUR),styrene-butadiene rubber (copolymer of styrene and butadiene, SBR),nitrile rubber (copolymer of butadiene and acrylonitrile, NBR), EPM(ethylene propylene rubber, a copolymer of ethylene and propylene), EPDMrubber (ethylene propylene diene rubber, a terpolymer of ethylene,propylene and a diene-component), epichlorohydrin rubber (ECO),polyacrylic rubber (ACM, ABR), silicone rubber (SI, Q, VMQ),fluorosilicone rubber (FVMQ), fluoroelastomers (FKM, and FEPM; such asViton, Tecnoflon, Fluorel, Aflas and Dai-El), perfluoroelastomers (FFKM:Tecnoflon PFR, Kalrez, Chemraz, Perlast), polyether block amides (PEBA),chlorosulfonated polyethylene (CSM; e.g. Hypalon), and ethylene-vinylacetate (EVA), thermoplastic elastomers (TPE), protein resilin, proteinelastin, ethylene oxide-epichlorohydrin copolymer, polyurethane,urethane-urea copolymer, and combinations thereof.

The urethane-urea copolymer film usually consists of two types ofdomains, soft domains and hard ones. Entangled linear backbone chainsconsisting of poly (tetramethylene ether) glycol (PTMEG) unitsconstitute the soft domains, while repeated methylene diphenyldiisocyanate (MDI) and ethylene diamine (EDA) units constitute the harddomains. The lithium ion-conducting additive can be incorporated in thesoft domains or other more amorphous zones.

The presently invented lithium secondary batteries can contain a widevariety of cathode active materials. The cathode active material layermay contain a cathode active material selected from an inorganicmaterial, an organic material, a polymeric material, or a combinationthereof.

The inorganic material may be selected from a metal oxide, metalphosphate, metal silicide, metal selenide, transition metal sulfide,sulfur, lithium polysulfide, selenium, lithium selenide, or acombination thereof.

The inorganic material may be selected from a lithium cobalt oxide,lithium nickel oxide, lithium manganese oxide, lithium vanadium oxide,lithium-mixed metal oxide, lithium iron phosphate, lithium manganesephosphate, lithium vanadium phosphate, lithium mixed metal phosphate,lithium metal silicide, or a combination thereof.

The inorganic material may be selected from a lithium transition metalsilicate, denoted as Li₂MSiO₄ or Li₂Ma_(x)Mb_(y)SiO₄, wherein M and Maare selected from Fe, Mn, Co, Ni, or V, Mb is selected from Fe, Mn, Co,Ni, V, Ti, Al, B, Sn, or Bi; and x+y≤1.

Examples of the lithium transition metal oxide- or lithium mixedtransition metal oxide-based positive active materials include:Li(M′_(X)M″_(Y))O₂, where M′ and M″ are different metals (e.g.,Li(Ni_(X)Mn_(Y))O₂, Li(Ni_(1/2)Mn_(1/2))O₂, Li(Cr_(X)Mn_(1-X))O₂,Li(Al_(X)Mn_(1-X))O₂), Li(Co_(X)M_(1-X))O₂, where M is a metal, (e.g.Li(Co_(X)Ni_(1-X))O₂ and Li(Co_(X)Fe_(1-X))O₂),Li_(1-W)(Mn_(X)Ni_(Y)Co_(Z))O₂, (e.g. Li(Co_(X)Mn_(Y)Ni_((1-X-Y)))O₂,Li(Mn_(1/3)Ni_(1/3)Co_(1/3))O₂, Li(Mn_(1/3)Ni_(1/3)Co_(1/3-X)Mg_(X))O₂,Li(Mn_(0.4)Ni_(0.4)Co_(0.2))O₂, Li(Mn_(0.1)Ni_(0.1)Co_(0.8))O₂),Li_(1-W)(Mn_(X)Ni_(X)Co_(1-2X))O₂, Li_(1-W)Mn_(X)Ni_(Y)CoAl_(W))O₂,Li_(1-W)(Ni_(X)Co_(Y)Al_(Z))O₂, where W=0-1, (e.g.,Li(Ni_(0.8)Co_(0.15)Al_(0.05))O₂), Li_(1-W)(Ni_(X)Co_(Y)M_(Z))O₂, whereM is a metal, Li_(1-W) (Ni_(X)Mn_(y)M_(Z))O₂, where M is a metal,Li(Ni_(X)Mn_(y)Cr_(2-X))O₄, LiM′M″₂O₄, where M′ and M″ are differentmetals (e.g., LiMn_(2-Y-Z)Ni_(Y)O₄, LiMn_(2-Y-Z)Ni_(Y)Li_(Z)O₄,LiMn_(1.5)Ni_(0.5)O₄, LiNiCuO₄, LiMn_(1-X)Al_(X)O₄,LiNi_(0.5)Ti_(0.5)O₄, Li_(1.05)Al_(0.1)Mn_(1.85)O_(4-z)F_(z), Li₂MnO₃)Li_(X)V_(Y)O_(Z), e.g. LiV₃O₈, LiV₂O₅, and LiV₆O₁₃. This list includesthe well-known lithium nickel cobalt manganese oxides (NCM) and lithiumnickel cobalt manganese aluminum oxides (NCM), among others.

The metal oxide contains a vanadium oxide selected from the groupconsisting of VO₂, Li_(x)VO₂, V₂O₅, Li_(x)V₂O₅, V₃O₈, Li_(x)V₃O_(s),Li_(x)V₃O₇, V₄O₉, Li_(x)V₄O₉, V₆O₁₃, Li_(x)V₆O₁₃, their doped versions,their derivatives, and combinations thereof, wherein 0.1<x<5.

In certain desired embodiments, the inorganic cathode active material isselected from a lithium-free cathode material. Such an initiallylithium-free cathode may contain a metal fluoride or metal chlorideincluding the group consisting of CoF₃, MnF₃, FeF₃, VF₃, VOF₃, TiF₃,BiF₃, NiF₂, FeF₂, CuF₂, CuF, SnF₂, AgF, CuCl₂, FeCl₃, MnCl₂, andcombinations thereof. In these cases, it is particularly desirable tohave the anode active material prelithiated to a high level, preferablyno less than 50%. In some preferred embodiments, prelithiated anodecomprises Si that is prelithiated to approximately 60-100% and thecathode comprises a cathode active material that is initiallylithium-free.

The inorganic cathode active material may be selected from: (a) bismuthselenide or bismuth telluride, (b) transition metal dichalcogenide ortrichalcogenide, (c) sulfide, selenide, or telluride of niobium,zirconium, molybdenum, hafnium, tantalum, tungsten, titanium, cobalt,manganese, iron, nickel, or a transition metal; (d) boron nitride, or(e) a combination thereof.

The inorganic material may be selected from a transition metaldichalcogenide, a transition metal trichalcogenide, or a combinationthereof. The inorganic material may be selected from TiS₂, TaS₂, MoS₂,NbSe₃, MnO₂, CoO₂, an iron oxide, a vanadium oxide, or a combinationthereof.

The metal oxide or metal phosphate may be selected from a layeredcompound LiMO₂, spinel compound LiM₂O₄, olivine compound LiMPO₄,silicate compound Li₂MSiO₄, Tavorite compound LiMPO₄F, borate compoundLiMBO₃, or a combination thereof, wherein M is a transition metal or amixture of multiple transition metals.

The organic material or polymeric material may be selected fromPoly(anthraquinonyl sulfide) (PAQS), a lithium oxocarbon,3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA),poly(anthraquinonyl sulfide), pyrene-4,5,9,10-tetraone (PYT),polymer-bound PYT, Quino(triazene), redox-active organic material,Tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE),2,3,6,7,10,11-hexamethoxytriphenylene (HMTP), poly(5-amino-1,4-dyhydroxyanthraquinone) (PADAQ), phosphazene disulfide polymer ([(NPS₂)₃]n),lithiated 1,4,5,8-naphthalenetetraol formaldehyde polymer,Hexaazatrinaphtylene (HATN), Hexaazatriphenylene hexacarbonitrile(HAT(CN)₆), 5-Benzylidene hydantoin, Isatine lithium salt, Pyromelliticdiimide lithium salt, tetrahydroxy-p-benzoquinone derivatives (THQLi₄),N,N′-diphenyl-2,3,5,6-tetraketopiperazine (PHP),N,N′-diallyl-2,3,5,6-tetraketopiperazine (AP),N,N′-dipropyl-2,3,5,6-tetraketopiperazine (PRP), a thioether polymer, aquinone compound, 1,4-benzoquinone, 5,7,12,14-pentacenetetrone (PT),5-amino-2,3-dihydro-1,4-dyhydroxy anthraquinone (ADDAQ),5-amino-1,4-dyhydroxy anthraquinone (ADAQ), calixquinone, Li₄C₆O₆,Li₂C₆O₆, Li₆C₆O₆, or a combination thereof.

The thioether polymer is selected fromPoly[methanetetryl-tetra(thiomethylene)](PMTTM),Poly(2,4-dithiopentanylene) (PDTP), a polymer containingPoly(ethene-1,1,2,2-tetrathiol) (PETT) as a main-chain thioetherpolymers, a side-chain thioether polymer having a main-chain consistingof conjugating aromatic moieties, and having a thioether side chain as apendant, Poly(2-phenyl-1,3-dithiolane) (PPDT),Poly(1,4-di(1,3-dithiolan-2-yl)benzene) (PDDTB),poly(tetrahydrobenzodithiophene) (PTHBDT),poly[1,2,4,5-tetrakis(propylthio)benzene] (PTKPTB, orpoly[3,4(ethylenedithio)thiophene] (PEDTT).

The organic material may contain a phthalocyanine compound selected fromcopper phthalocyanine, zinc phthalocyanine, tin phthalocyanine, ironphthalocyanine, lead phthalocyanine, nickel phthalocyanine, vanadylphthalocyanine, fluorochromium phthalocyanine, magnesium phthalocyanine,manganous phthalocyanine, dilithium phthalocyanine, aluminumphthalocyanine chloride, cadmium phthalocyanine, chlorogalliumphthalocyanine, cobalt phthalocyanine, silver phthalocyanine, ametal-free phthalocyanine, a chemical derivative thereof, or acombination thereof.

The working electrolyte used in the lithium battery may be a liquidelectrolyte, polymer gel electrolyte, solid-state electrolyte (includingsolid polymer electrolyte, inorganic electrolyte, and compositeelectrolyte), quasi-solid electrolyte, ionic liquid electrolyte. Theliquid electrolyte or polymer gel electrolyte typically comprises alithium salt dissolved in an organic solvent or ionic liquid solvent.There is no particular restriction on the types of lithium salt orsolvent that can be used in practicing the present inventions.

There are a wide variety of processes that can be used to produce layersof polymer composite separators. These include coating, casting,painting, spraying (e.g., ultrasonic spraying), spray coating, printing(screen printing, 3D printing, etc.), tape casting, extrusion, etc.

The disclosure also provides a process for manufacturing the polymercomposite separator described above. As illustrated in FIG. 5(A), theprocess comprising (A) dispersing particles or fibers of the inorganicsolid material or polymer fibers and the lithium salt in the firstliquid solvent to form a liquid reactive mass or reactive slurry (theoptional second liquid solvent may be added or mixed into the firstliquid solvent at this stage); (B) dispensing and depositing a layer ofthe liquid reactive mass onto a solid substrate surface; and (C)polymerizing and/or curing the reactive mass to form the layer ofpolymer composite separator. Alternatively, the second liquid solventmay be added after the polymerization/crosslinking step.

This reactive mass (a precursor to the desired polymer) may comprise amonomer, an oligomer, or an uncured (but curable) polymer possiblydissolved in a liquid solvent where necessary. This precursor issubsequently cured (polymerized and/or crosslinked).

The solid substrate may be an anode current collector, an anode activematerial layer, or a cathode active material layer. In other words, thispolymer composite separator can be directly deposited onto a layer ofanode active material, an anode current collector, or a layer of cathodeactive material. This is achievable because curing of the polymer doesnot require a high temperature; curing temperature typically lower than300° C. or even lower than 100° C. This is in stark contrast to thetypically 900-1,200° C. required of sintering an inorganic solidelectrolyte to form a ceramic separator. In addition, the presentlydisclosed separator is at least as good as a ceramic separator in termsof reducing interfacial impedance and stopping dendrite penetration.

Preferably, the process is a roll-to-roll process wherein step (B)comprises (i) continuously feeding a layer of the solid substrate (e.g.flexible metal film, plastic film, etc.) from a feeder roller to adispensing zone where the reactive mass is dispensed and deposited ontothe solid substrate to form a continuous layer of the reactive mass;(ii) moving the layer of the reactive mass into a reacting zone wherethe reactive mass is exposed to heat, ultraviolet (UV) light, orhigh-energy radiation (e.g., electron beam) to polymerize and/or curethe reactive mass to form a continuous layer of polymer composite; and(iii) collecting the polymer composite on a winding roller. This processis conducted in a reel-to-reel manner.

In certain embodiments, as illustrated in FIG. 4 , the roll-to-rollprocess may begin with continuously feeding a solid substrate layer 12(e.g., PET film) from a feeder roller 10. A dispensing device 14 isoperated to dispense and deposit a reactive mass 16 (e.g. slurry) ontothe solid substrate layer 12, which is driven toward a pair of rollers(18 a, 18 b). These rollers are an example of a provision to regulate orcontrol the thickness of the reactive mass 20. The reactive mass 20,supported on the solid substrate, is driven to move through a reactingzone 22 which is provided with a curing means (heat, UV, high energyradiation, etc.). The partially or fully cured polymer composite 24 iscollected on a winding roller 26. One may unwind the roll at a laterstage.

The process may further comprise cutting and trimming the layer ofpolymer composite into one or multiple pieces of polymer compositeseparators. The process may further comprise combining an anode, thepolymer composite separator, an electrolyte, and a cathode electrode toform a lithium battery.

As illustrated in FIG. 5(B), the disclosure further provides a processfor manufacturing the polymer composite separator described above, theprocess comprising (A) forming a woven or nonwoven fabric comprising atleast one of the polymer fibers and inorganic material fibers, andoptional particles of the inorganic solid material; (B) dissolving ordispersing the lithium salt and the initiator or crosslinking agent inthe first liquid solvent to form a liquid reactive mass (a second liquidsolvent may be added at this stage); (C) impregnating or infiltrating adesired amount of the liquid reactive mass into the fabric; and (D)polymerizing and/or crosslinking said reactive mass to form the layer ofpolymer composite separator. The process may further comprise a step (E)of combining an anode, the woven or nonwoven fabric, and a cathode toform a lithium battery cell, wherein step (C) or both steps (C) and (D)are conducted either before or after step (E).

In other words, the liquid reactive mass may be impregnated into thefabric and cured to form a polymer composite separator before thisseparator is combined with an anode and a cathode, along with otherdesired components, into a battery cell. Alternatively, one may chooseto combine an anode, a layer of the woven or nonwoven fabric, and acathode to form a dry lithium battery cell, which is followed byinjection of the reactive mass into the dry cell and curing the reactivemass in situ (the liquid reactive mass permeates into the fabric and theanode and the cathode active layers and get cured thereafter).

The lithium battery may be a lithium metal battery, lithium-ion battery,lithium-sulfur battery, lithium-selenium battery, lithium-air battery,etc. The cathode active material in the lithium-sulfur battery maycomprise sulfur or lithium polysulfide.

Example 1: Preparation of Solid Electrolyte Powder, Lithium NitridePhosphate Compound (LIPON)

Particles of Li₃PO₄ (average particle size 4 μm) and urea were preparedas raw materials; 5 g each of Li₃PO₄ and urea was weighed and mixed in amortar to obtain a raw material composition. Subsequently, the rawmaterial composition was molded into 1 cm×1 cm×10 cm rod with a moldingmachine, and the obtained rod was put into a glass tube and evacuated.The glass tube was then subjected to heating at 500° C. for 3 hours in atubular furnace to obtain a lithium nitride phosphate compound (LIPON).The compound was ground in a mortar into a powder form.

Example 2: Preparation of Solid Electrolyte Powder, Lithium SuperionicConductors with the Li₁₀GeP₂S₁₂ (LGPS)-Type Structure

The starting materials, Li₂S and SiO₂ powders, were milled to obtainfine particles using a ball-milling apparatus. These starting materialswere then mixed together with P₂S₅ in the appropriate molar ratios in anAr-filled glove box. The mixture was then placed in a stainless steelpot, and milled for 90 min using a high-intensity ball mill. Thespecimens were then pressed into pellets, placed into a graphitecrucible, and then sealed at 10 Pa in a carbon-coated quartz tube. Afterbeing heated at a reaction temperature of 1,000° C. for 5 h, the tubewas quenched into ice water. The resulting solid electrolyte materialwas then subjected to grinding in a mortar to form a powder sample to belater added as inorganic solid electrolyte particles dispersed in anintended polymer matrix of a composite separator (examples ofbinder/matrix polymers are given below).

Example 3: Preparation of Garnet-Type Solid Electrolyte Powder

The synthesis of the c-Li_(6.25)Al_(0.25)La₃Zr₂O₁₂ was based on amodified sol-gel synthesis-combustion method, resulting insub-micron-sized particles after calcination at a temperature of 650° C.(J. van den Broek, S. Afyon and J. L. M. Rupp, Adv. Energy Mater., 2016,6, 1600736).

For the synthesis of cubic garnet particles of the compositionc-Li_(6.25)Al_(0.25)La₃Zr₂O₁₂, stoichiometric amounts of LiNO₃,Al(NO₃)₃-9H₂O, La(NO₃)₃-6(H₂O), and zirconium (IV) acetylacetonate weredissolved in a water/ethanol mixture at temperatures of 70° C. To avoidpossible Li-loss during calcination and sintering, the lithium precursorwas taken in a slight excess of 10 wt % relative to the otherprecursors. The solvent was left to evaporate overnight at 95° C. toobtain a dry xerogel, which was ground in a mortar and calcined in avertical tube furnace at 650° C. for 15 h in alumina crucibles under aconstant synthetic airflow. Calcination directly yielded the cubic phasec-Li_(6.25)Al_(0.25)La₃Zr₂O₁₂, which was ground to a fine powder in amortar for further processing.

The c-Li_(6.25)Al_(0.25)La₃Zr₂O₁₂ solid electrolyte pellets withrelative densities of ˜87±3% made from this powder (sintered in ahorizontal tube furnace at 1070° C. for 10 h under O₂ atmosphere)exhibited an ionic conductivity of ˜0.5×10⁻³ S cm⁻¹ (RT). Thegarnet-type solid electrolyte with a composition ofc-Li_(6.25)Al_(0.25)La₃Zr₂O₁₂ (LLZO) in a powder form was dispersed inseveral polymers discussed in the examples below.

Example 4: Preparation of Sodium Superionic Conductor (NASICON) TypeSolid Electrolyte Powder

The Na_(3.1)Zr_(1.95)M_(0.05)Si₂PO₁₂ (M=Mg, Ca, Sr, Ba) materials weresynthesized by doping with alkaline earth ions at octahedral6-coordination Zr sites. The procedure employed includes two sequentialsteps. Firstly, solid solutions of alkaline earth metal oxides (MO) andZrO₂ were synthesized by high energy ball milling at 875 rpm for 2 h.Then NASICON Na_(3.1)Zr_(1.95)M_(0.05)Si₂PO₁₂ structures weresynthesized through solid-state reaction of Na₂CO₃,Zr_(1.95)M_(0.05)O_(3.95), SiO₂, and NH₄H₂PO₄ at 1260° C.

Example 5: Lithium Metal Cell Featuring an In Situ Polymerized VC as theFirst Liquid Solvent and TEP as a Second Liquid Solvent in an AramidNonwoven Fabric Layer and the Cell

In one example, vinylene carbonate (VC) as a first liquid solvent, TEPas a second liquid solvent (flame retardant), and poly(ethylene glycol)diacrylate (PEGDA, as a crosslinking agent) were stirred under theprotection of argon gas until a homogeneous solution was obtained. TheTEP has the following chemical structure:

Subsequently, lithium hexafluoro phosphate, as a lithium salt, was addedand dissolved in the above solution to obtain a reactive mixturesolution, wherein the weight fractions of VC, TEP, polyethylene glycoldiacrylate, and lithium hexafluoro phosphate were 80 wt %, 5 wt %, 10 wt%, and 5 wt %, respectively.

A lithium metal cell was made, comprising a lithium metal foil as theanode active material, a cathode comprising LiCoO₂, and a separatorbackbone composed of particles of Li₇La₃Zr₂O₁₂ embedded in an aramidfiber-based nonwoven fabric layer. This cell was then injected with thereactive solution mixture (10% by weight based on the total cellweight). The cell was then irradiated with electron beam at roomtemperature until a total dosage of 40 Gy was reached. In-situpolymerization of the polymerizable first liquid solvent in the batterycell was accomplished, resulting in a quasi-solid electrolyte thatpermeates into the cathode to wet the surfaces of LiCoO₂ particles,impregnates the porous separator layer (nonwoven fabric), and comes incontact with the lithium metal in the anode.

Additionally, particles of Li₇La₃Zr₂O₂ were mixed and dispersed in aliquid mixture of VC and TEP (0-30% TEP) to form reactive compositelayers having a thickness from 5 to 35 μm. These reactive layers werethen cured under comparable conditions as above to obtain free-standingpolymer composite separator layers.

Example 6: VC as the Polymerizable First Solvent and an UnsaturatedPhosphazene as a Second Solvent

Similar procedure as in Example 1 was followed, but the second liquidsolvent was an unsaturated phosphazene (UPA) having the followingstructure:

This UPA was synthesized according to a procedure reported by Mason K.Harrup, et al. “Unsaturated phosphazenes as co-solvents for lithium-ionbattery electrolytes,” Journal of Power Sources 278 (2015) 794-801. TheVC/UPA or FEC/UPA ratio was varied as 25/75, 50/50, and 75/25.

Example 7: VC as the First Liquid Solvent and Trifluoro-Phosphate (TFP)as the Second Liquid Solvent

In this study, VC was used as the first liquid solvent,azodiisobutyronitrile (AIBN) as the initiator, lithium difluoro(oxalate)borate (LiDFOB) as the lithium salt, and TFP as the secondflame-retardant liquid solvent. TFP has the following chemicalstructure:

Solutions containing 1.5 M LiDFOB in VC and 0.2 wt % AIBN (vs VC) wereprepared. Then, TFP (TFP/VC ratios being from 10/90 to 50/50) was addedinto the solution to form mixed electrolyte solutions. The electrolytesolutions were separately injected into different dry battery cells,allowing the electrolyte solution to permeate into the anode (wettingout the anode active material; e.g., graphite particles), into thecathode (wetting out the cathode active material; e.g., NCM-532particles), and into the porous separator layer (porous nonwoven of PANnano-fibers and LIPON-type inorganic solid electrolyte particles). Thebattery cells were stored at 60° C. for 24 h and then 80° C. for another2 h to obtain polymerized VC that contained TFP in their matrix ofpolymer chains. The polymerization scheme of VC is shown below (Reactionscheme 1):

Example 8: Vinyl Ethylene Sulfite (VES) as the First Solvent andHydrofluoro Ether (HFE) as the Second Solvent

Under the protection of an argon gas atmosphere, vinyl ethylene sulfite(VES), hydrofluoro ether (HFE), and tetra(ethylene glycol) diacrylateswere stirred evenly to form a solution. Bis trifluoromethyl sulfimidelithium was then dissolved in the solution to obtain a solution mixture.In this solution mixture, the weight fractions for the four ingredientswere VEC (40%). HFE (20%), tetra(ethylene glycol) diacrylates (20%), andbis trifluoromethyl sulfimide (10%).

The mixed solution (reactive mass) was added to a lithium-ion cellhaving an NCM cathode, graphite anode, and porous SiO₂/glass fibers mat.After the mixed solution was injected, the mixed solution accounted for3% of the total cell weight. The cell was exposed to electron beam at50° C. until a dosage of 20 kGy was reached. VEC was polymerized andcrosslinked to become a solid polymer, but FIFE remained as a liquid.

On a separate basis, several pieces of porous SiO/glass fiber mat weredipped into the reactive mass (without HFE) and cured under the sameconditions to obtain polymer composite separator layers. Additionally,one of such polymer composite layers was coated with a layer ofVEC-based reactive mass and then cured so that there was a layer of neatpolymer (free of any inorganic particles or fibers) on one side of theresulting composite separator layer.

Example 9: Lithium-Ion Cell Featuring an In Situ Polymerized PhenylVinyl Sulfide (PVS) in the Presence of a Second Solvent TMS (PVS/TMSRatio=9/1-10/0)

TMS has the following chemical formula:

The lithium-ion cells prepared in this example comprise an anode ofmeso-carbon micro-beads (MCMB, a type of artificial graphite suppliedfrom China Steel Chemical Co., Taiwan), a cathode of NCM-622 particles,and a porous nonwoven fabric of aramid fibers partially impregnated withpoly(vinylidene fluoride)-hexafluoropropylene as a separator.

Phenyl vinyl sulfide (first liquid solvent), TMS (second solvent), CTA(chain transfer agent, shown below), AIBN (initiator, 1.0%), and 5% byweight of lithium trifluoro-methanesulfonate (LiCF₃SO₃) were mixed toform a reactive liquid mass. This reactive liquid mass was injected intothe lithium-ion cell, and heated at 60° C. to obtain a battery cellcontaining an in situ cued polymer electrolyte. Additionally, a polymercomposite separator was made by impregnating the reactive liquid massinto the pores of a layer of porous nonwoven fabric of aramid fiberspartially impregnated with (bonded by) poly(vinylidenefluoride)-hexafluoropropylene. This was followed by curing undercomparable conditions.

Example 10: Lithium-Ion Cell Featuring a Separator Comprising In SituPolymerized Phenyl Vinyl Sulfone

The lithium-ion cells prepared in this example comprise an anode ofgraphene-protected Si particles, a cathode of NCM-622 particles, and aporous membrane comprising particles of NASICON(Na_(3.1)Zr_(1.95)M_(0.05)Si₂PO₁₂) bonded together by a pentaerythritoltetraacrylate-based polymer.

Phenyl vinyl sulfone (PVS) can be polymerized with several anionic-typeinitiators; e.g., n-BuLi, ZnEt₂, LiN(CH₂)₂, and NaNH₂. The secondsolvent may be selected from pyridine, sulfolane, Trimethyl phosphate(TMP), Trifluoro-Phosphate (TFP), etc. Trimethyl phosphate has thefollowing chemical structure:

A mixture of PVS, TFP, n-BuLi (1.0% relative to PVS), and LiBF₄ (0.5 M)was thoroughly mixed and injected into the battery cell, which wasmaintained at 30° C. overnight to cure the polymer.

In conclusion, the in situ cured polymer composite-based separatorstrategy is surprisingly effective in alleviating the problems oflithium metal dendrite formation and lithium metal-electrolyte reactionsthat otherwise lead to rapid capacity decay and potentially internalshorting and explosion of the lithium secondary batteries. The presenceof a small amount of a second liquid solvent may be designed to imparthigh lithium-ion conductivity to the polymer. This second liquid mayalso help to maintain a good contact between the current collector (orthe deposited lithium film during the charging procedure) and theseparator, enabling uniform re-deposition of lithium ions withoutinterruption.

We claim:
 1. A flame-resistant polymer composite separator for use in alithium battery, wherein the polymer composite separator comprises (a) abinder or matrix polymer; (b) 0.1% to 50% by weight of a lithium saltdispersed in the polymer; and (c) from 30% to 99% by weight of particlesor fibers of an inorganic material or polymer fibers that are dispersedin or bonded by the polymer, wherein the polymer is a polymerization orcrosslinking product of a reactive additive comprising (i) a firstliquid solvent that is polymerizable, (ii) an initiator or crosslinkingagent, and (iii) the lithium salt and wherein the polymer compositeseparator has a thickness from 50 nm to 100 μm and a lithium ionconductivity from 10⁻⁸ S/cm to 5×10⁻² S/cm at room temperature.
 2. Thepolymer composite separator of claim 1, wherein the first liquid solventis selected from the group consisting of vinylene carbonate, ethylenecarbonate, fluoroethylene carbonate, vinyl sulfite, vinyl ethylenesulfite, vinyl ethylene carbonate, 1,3-propyl sultone, 1,3,5-trioxane(TXE), 1,3-acrylic-sultones, methyl ethylene sulfone, methyl vinylsulfone, ethyl vinyl sulfone, methyl methacrylate, vinyl acetate,acrylamide, 1,3-dioxolane (DOL), fluorinated ethers, fluorinated esters,sulfones, sulfides, dinitriles, acrylonitrile (AN), sulfates, siloxanes,silanes, N-methylacetamide, acrylates, ethylene glycols,tetrahydrofuran, combinations thereof, and combinations thereof withphosphates, phosphonates, phosphinates, phosphines, phosphine oxides,phosphonic acids, phosphorous acid, phosphites, phosphoric acids,phosphazene compounds, ionic liquids, derivatives thereof, and mixturesthereof.
 3. The polymer composite separator of claim 1, wherein saidinorganic material comprises particles of an inorganic solid electrolytematerial selected from an oxide type, sulfide type, hydride type, halidetype, borate type, phosphate type, lithium phosphorus oxynitride(LiPON), Garnet-type, lithium superionic conductor (LISICON) type,sodium superionic conductor (NASICON) type, or a combination thereof. 4.The polymer composite separator of claim 1, wherein said inorganicmaterial particles comprise a material selected from a transition metaloxide, aluminum oxide, silicon dioxide, transition metal sulfide,transition metal selenide, alkylated ceramic particles, metal phosphate,metal carbonate, or a combination thereof, or the inorganic materialfibers are selected from ceramic fibers, glass fibers, or a combinationthereof.
 5. The polymer composite separator of claim 1, wherein saidpolymer fibers comprise polymeric materials selected from the groupconsisting essentially of polyacrylonitriles, polyolefins, polyolefincopolymers, polyamides, polyimides, polyvinyl alcohol, polyethyleneterephthalate, polybutylene terephthalate, polysulfone, polyvinylfluoride, polyvinylidene fluoride, polyvinylidenefluoride-hexafluoropropylene, polymethyl pentene, polyphenylene sulfide,polyacetyl, polyurethane, aromatic polyamide, semi-aromatic polyamide,polypropylene terephthalate, polymethyl methacrylate, polystyrene,synthetic cellulosic polymers, polyaramids, rigid-rod polymers, ladderpolymers, and blends, mixtures and copolymers including said polymericmaterials.
 6. The polymer composite separator of claim 1, wherein saidlithium salt is selected from lithium perchlorate, LiClO₄, lithiumhexafluorophosphate, LiPF₆, lithium borofluoride, LiBF₄, lithiumhexafluoroarsenide, LiAsF₆, lithium trifluoro-methanesulfonate,LiCF₃SO₃, bis-trifluoromethyl sulfonylimide lithium, LiN(CF₃SO₂)₂,lithium bis(oxalato)borate, LiBOB, lithium oxalyldifluoroborate,LiBF₂C₂O₄, lithium nitrate, LiNO₃, Li-fluoroalkyl-phosphates,LiPF₃(CF₂CF₃)₃, lithium bisperfluoro-ethylsulfonylimide, LiBETI, lithiumbis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide,lithium trifluoromethanesulfonimide (LiTFSI), an ionic liquid-basedlithium salt, Li₂CO₃, Li₂O, Li₂C₂O₄, LiOH, LiX, ROCO₂Li, HCOLi, ROLi,(ROCO₂Li)₂, (CH₂OCO₂Li)₂, Li₂S, Li_(x)SO_(y), or a combination thereof,wherein X=F, Cl, I, or Br, R=a hydrocarbon group, x=0-1, y=1-4.
 7. Thepolymer composite separator of claim 1, wherein the polymer forms amixture, blend, copolymer, or interpenetrating network with a lithiumion-conducting polymer selected from poly(ethylene oxide), polypropyleneoxide, polyoxymethylene, polyvinylene carbonate, polypropylenecarbonate, poly(ethylene glycol), poly(acrylonitrile), poly(methylmethacrylate), poly(vinylidene fluoride), poly bis-methoxyethoxyethoxide-phosphazene, polyvinyl chloride, polydimethylsiloxane,poly(vinylidene fluoride)-hexafluoropropylene, cyanoethyl poly(vinylalcohol), a pentaerythritol tetraacrylate-based polymer, an aliphaticpolycarbonate, a single Li-ion conducting solid polymer with acarboxylate anion, a sulfonylimide anion, or sulfonate anion,poly(ethylene glycol) diacrylate, poly(ethylene glycol) methyl etheracrylate, polyurethane, polyurethan-urea, polyacrylamide, a polyionicliquid, polymerized 1,3-dioxolane, polyepoxide ether, polysiloxane,poly(acrylonitrile-butadiene), polynorbornene, poly(hydroxyl styrene),poly(ether ether ketone), polypeptoid, poly(ethylene-maleic anhydride),polycaprolactone, poly(trimethylene carbonate), a copolymer thereof, asulfonated derivative thereof, or a combination thereof.
 8. The polymercomposite separator of claim 1, further comprising a second liquidsolvent that permeates into the separator wherein the second liquidsolvent has a higher flash point or lower vapor pressure as compared tothe first liquid solvent.
 9. The polymer composite separator of claim 8,wherein the second liquid solvent is selected from the group consistingof fluoroethylene carbonate, vinyl sulfite, vinyl ethylene sulfite,1,3-propyl sultone, 1,3,5-trioxane (TXE), 1,3-acrylic-sultones, methylethylene sulfone, methyl vinyl sulfone, ethyl vinyl sulfone, methylmethacrylate, vinyl acetate, acrylamide, 1,3-dioxolane (DOL),fluorinated ethers, fluorinated esters, fluorinated vinyl esters,fluorinated vinyl ethers, sulfones, sulfides, dinitriles, acrylonitrile(AN), sulfates, siloxanes, silanes, N-methylacetamide, acrylates,ethylene glycols, tetrahydrofuran, phosphates, phosphonates,phosphinates, phosphines, phosphine oxides, phosphonic acids,phosphorous acid, phosphites, phosphoric acids, phosphazene compounds,ionic liquids, derivatives thereof, and mixtures thereof.
 10. Thepolymer composite separator of claim 8, wherein the first or the secondliquid solvent comprises a sulfone or sulfide selected from vinylsulfone, allyl sulfone, alkyl vinyl sulfone, aryl vinyl sulfone, vinylsulfide, TrMS, MTrMS, TMS, EMS, MMES, EMES, EMEES, or a combinationthereof:


11. The polymer composite separator of claim 10, wherein the vinylsulfone or sulfide is selected from ethyl vinyl sulfide, allyl methylsulfide, phenyl vinyl sulfide, phenyl vinyl sulfoxide, allyl phenylsulfone, allyl methyl sulfone, divinyl sulfone, or a combinationthereof.
 12. The polymer composite separator of claim 8, wherein thefirst or the second liquid solvent comprises a nitrile, a dinitrileselected from AND, GLN, or SEN, or a combination thereof:


13. The polymer composite separator of claim 8, wherein the first or thesecond liquid solvent comprises a phosphate selected from allyl-type,vinyl-type, styrenic-type and (meth)acrylic-type monomers bearing aphosphonate moiety.
 14. The polymer composite separator of claim 8,wherein the first liquid solvent or the second liquid solvent isselected from the group consisting of 2-alkoxy (orphenoxy)-2-oxo-1,3,2-dioxaphospholane (I) and 2-alkoxy (orphenoxy)-2-oxo-1,3,2-dioxaphosphorinane (II), derivatives thereof, andcombinations thereof:


15. The polymer composite separator of claim 8, wherein the first liquidsolvent or the second liquid solvent comprises phosphate, phosphonate,phosphonic acid, or phosphite selected from TMP, TEP, TFP, TDP, DPOF,DMMP, DMMEMP, tris(trimethylsilyl)phosphite (TTSPi), alkyl phosphate,triallyl phosphate (TAP), a combination thereof, wherein TMP, TEP, TFP,TDP, DPOF, DMMP, and DMMEMP have the following chemical formulae:

wherein an end group thereof or a functional group attached thereofcomprises unsaturation for polymerization.
 16. The polymer compositeseparator of claim 8, wherein the first liquid solvent or the secondliquid solvent comprises phosphonate vinyl monomer selected from thegroup consisting of phosphonate bearing allyl monomers, phosphonatebearing vinyl monomers, phosphonate bearing styrenic monomers,phosphonate bearing (meth)acrylic monomers, vinylphosphonic acids, andcombinations thereof.
 17. The polymer composite separator of claim 16,wherein the phosphonate bearing allyl monomer is selected from a Dialkylallylphosphonate monomer or Dioxaphosphorinane allyl monomer; thephosphonate bearing vinyl monomers is selected from a Dialkyl vinylphosphonate monomer or Dialkyl vinyl ether phosphonate monomer; thephosphonate bearing styrenic monomer is selected from α-, β-, orp-vinylbenzyl phosphonate monomers; or the phosphonate bearing(meth)acrylic monomer is selected from a monomer having a phosphonategroup linked to the acrylate double bond, a phosphonate groups linked tothe ester, or a phosphonate groups linked to the amide.
 18. The polymercomposite separator of claim 1, wherein the crosslinking agent comprisesa compound having at least one reactive group selected from a hydroxylgroup, an amino group, an imino group, an amide group, an acrylic amidegroup, an amine group, an acrylic group, an acrylic ester group, or amercapto group in the molecule.
 19. The polymer composite separator ofclaim 1, wherein the crosslinking agent is selected from poly(dicthanol)diacrylate, poly(ethyleneglycol)dimethacrylate, poly(diethanol)dimethylacrylate, poly(ethylene glycol) diacrylate, or a combinationthereof.
 20. The polymer composite separator of claim 1, wherein theinitiator is selected from an azo compound, azobisisobutyronitrile,azobisisoheptonitrile, dimethyl azobisisobutyrate, benzoyl peroxidetert-butyl peroxide and methyl ethyl ketone peroxide, benzoyl peroxide(BPO), bis(4-tert-butylcyclohexyl)peroxydicarbonate, t-amylperoxypivalate, 2,2′-azobis-(2,4-dimethylvaleronitrile),2,2′-azobis-(2-methylbutyronitrile),1,1-azobis(cyclohexane-1-carbonitrile, benzoylperoxide (BPO), hydrogenperoxide, dodecamoyl peroxide, isobutyryl peroxide, cumenehydroperoxide, tert-butyl peroxypivalate, diisopropyl peroxydicarbonate,lithium hexafluorophosphate (LiPF₆), lithium borofluoride (LiBF₄),lithium hexafluoroarsenide (LiAsF₆), lithium trifluoro-methanesulfonate(LiCF₃SO₃), bis-trifluoromethyl sulfonylimide lithium (LiN(CF₃SO₂)₂),lithium bis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate(LiBF₂C₂O₄), or a combination thereof.
 21. The polymer compositeseparator of claim 1, wherein said inorganic material particles arenon-uniformly distributed in the polymer matrix in such a manner that aconcentration of the inorganic material particles in one region of thepolymer matrix is greater than a concentration of the inorganic materialparticles in another region.
 22. The polymer composite separator ofclaim 21, wherein a concentration of the inorganic material particles inone surface region of the polymer matrix is at least 60% by volume andis greater than a concentration of the inorganic material particles in acore region of the polymer matrix.
 23. The polymer composite separatorof claim 1, wherein the particles or fibers of an inorganic materialand/or polymer fibers are in a woven or nonwoven fabric form.
 24. Alithium secondary battery comprising a cathode, an anode, and theflame-resistant polymer composite separator of claim 1 disposed betweenthe cathode and the anode.
 25. The lithium secondary battery of claim24, wherein the battery is a lithium metal battery and the anode has ananode current collector but initially the anode has no lithium orlithium alloy as an anode active material supported by said anodecurrent collector when the battery is made and prior to a charge ordischarge operation of the battery.
 26. The lithium secondary battery ofclaim 24, wherein the battery is a lithium metal battery and the anodehas an anode current collector and an amount of lithium or lithium alloyas an anode active material supported by said anode current collector.27. The lithium secondary battery of claim 24, wherein the battery is alithium-ion battery and the anode has an anode current collector and alayer of an anode active material supported by said anode currentcollector, wherein the anode active materials is selected from the groupconsisting of: (a) silicon (Si), germanium (Ge), tin (Sn), lead (Pb),antimony (Sb), phosphorus (P), bismuth (Bi), zinc (Zn), aluminum (Al),titanium (Ti), nickel (Ni), cobalt (Co), and cadmium (Cd); (b) alloys orintermetallic compounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Ni, Co,or Cd with other elements; (c) oxides, carbides, nitrides, sulfides,phosphides, selenides, and tellurides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al,Ti, Fe, Ni, Co, V, or Cd, and their mixtures, composites, orlithium-containing composites; (d) salts and hydroxides of Sn; (e)lithium titanate, lithium manganate, lithium aluminate, lithium titaniumniobium oxide, lithium-containing titanium oxide, lithium transitionmetal oxide, ZnCo₂O₄; (f) carbon or graphite particles (g) prelithiatedversions thereof; and (h) combinations thereof.
 28. The lithiumsecondary battery of claim 24, wherein said battery further comprises,in addition to the solid electrolyte in the separator, a workingelectrolyte in ionic contact with an anode active material and/or acathode active material wherein said working electrolyte is selectedfrom an organic liquid electrolyte, ionic liquid electrolyte, polymergel electrolyte, polymer solid electrolyte, solid-state inorganicelectrolyte, quasi-solid electrolyte having a lithium salt dissolved inan organic or ionic liquid with a lithium salt concentration higher than2.0 M, or a combination thereof.
 29. The lithium secondary battery ofclaim 24, wherein the polymer is also present in the anode or thecathode and the polymer comprises the lithium salt dispersed therein.30. The lithium secondary battery of claim 24, wherein said cathodecomprises a cathode active material selected from an inorganic material,an organic material, a polymeric material, or a combination thereof. 31.The lithium secondary battery of claim 30, wherein said inorganicmaterial, as a cathode active material, is selected from a metal oxide,metal phosphate, metal silicide, metal selenide, transition metalsulfide, metal fluoride, metal chloride, or a combination thereof. 32.The lithium secondary battery of claim 30, wherein said inorganiccathode active material is selected from a lithium cobalt oxide, lithiumnickel oxide, lithium manganese oxide, lithium vanadium oxide,lithium-mixed metal oxide, lithium iron phosphate, lithium manganesephosphate, lithium vanadium phosphate, lithium mixed metal phosphate,lithium metal silicide, or a combination thereof.
 33. The lithiumsecondary battery of claim 30, wherein said inorganic cathode activematerial is selected from a lithium transition metal silicate, denotedas Li₂MSiO₄ or Li₂Ma_(x)Mb_(y)SiO₄, wherein M and Ma are selected fromFe, Mn, Co, Ni, V, or VO; Mb is selected from Fe, Mn, Co, Ni, V, Ti, Al,B, Sn, or Bi; and x+y≤1.
 34. The lithium secondary battery of claim 30,wherein said cathode active material is selected from lithium nickelmanganese oxide (LiNi_(a)Mn_(2-a)O₄, 0<a<2), lithium nickel manganesecobalt oxide (LiNi_(n)Mn_(m)Co_(1-n-m)O₂, 0<n<1, 0<m<1, n+m<1), lithiumnickel cobalt aluminum oxide (LiNi_(c)CoAl_(1-c-d)O₂, 0<c<1, 0<d<1,c+d<1), lithium manganate (LiMn₂O₄), lithium iron phosphate (LiFePO₄),lithium manganese oxide (LiMnO₂), lithium cobalt oxide (LiCOO₂), lithiumnickel cobalt oxide (LiNi_(p)Co_(1-p)O₂, 0<p<1), or lithium nickelmanganese oxide (LiNi_(q)Mn_(2-q)O₄, 0<q<2).
 35. The lithium secondarybattery of claim 31, wherein said metal oxide or metal phosphate isselected from a layered compound LiMO₂, spinel compound LiM₂O₄, olivinecompound LiMPO₄, silicate compound Li₂MSiO₄, Tavorite compound LiMPO₄F,borate compound LiMBO₃, or a combination thereof, wherein M is atransition metal or a mixture of multiple transition metals.
 36. Aprocess for manufacturing the polymer composite separator of claim 1,the process comprising (A) dispersing particles or fibers of theinorganic solid material or polymer fibers and the lithium salt in thefirst liquid solvent to form a liquid reactive mass or reactive slurry;(B) dispensing and depositing a layer of said liquid reactive mass ontoa solid substrate surface; and (C) polymerizing and/or curing saidreactive mass to form said layer of polymer composite separator.
 37. Theprocess of claim 36, wherein said solid substrate is an anode currentcollector, an anode active material layer, or a cathode active materiallayer.
 38. The process of claim 36, which is a roll-to-roll processwherein said step (B) comprises (i) continuously feeding a layer of saidsolid substrate from a feeder roller to a dispensing zone where saidreactive mass is dispensed and deposited onto said solid substrate toform a continuous layer of said reactive mass; (ii) moving said layer ofthe reactive mass into a reacting zone where the reactive mass isexposed to heat, ultraviolet light, or high-energy radiation topolymerize and/or cure said reactive mass to form a continuous layer ofpolymer composite; and (iii) collecting said polymer composite on awinding roller.
 39. The process of claim 38, further comprising cuttingand trimming said layer of polymer composite into one or multiple piecesof polymer composite separators.
 40. The process of claim 38, furthercomprising a step of combining an anode, said polymer compositeseparator, an electrolyte, and a cathode electrode to form a lithiumbattery.
 41. A process for manufacturing the polymer composite separatorof claim 1, the process comprising (A) forming a woven or nonwovenfabric comprising at least one of the polymer fibers and inorganicmaterial fibers, and particles of the inorganic solid material; (B)dissolving or dispersing the lithium salt and the initiator orcrosslinking agent in the first liquid solvent to form a liquid reactivemass; (C) impregnating or infiltrating a desired amount of the liquidreactive mass into the fabric; and (D) polymerizing and/or crosslinkingsaid reactive mass to form said layer of polymer composite separator.42. The process of claim 41, further comprising a step (E) of combiningan anode, the woven or nonwoven fabric, and a cathode to form a lithiumbattery cell, wherein step (C) or both steps (C) and (D) are conductedeither before or after step (E).